Fact-checked by Grok 2 weeks ago

Phyllite

Phyllite is a fine-grained, foliated metamorphic rock that develops a distinctive silky or satiny sheen on its cleavage surfaces due to the alignment of tiny platy mica minerals, such as muscovite and biotite, which reflect light.^[1] It typically forms through low- to medium-grade regional metamorphism of pre-existing sedimentary rocks like shale or mudstone, under temperatures ranging from 300°C to 450°C and relatively low pressures, where clay minerals recrystallize into these micas without significant grain coarsening.^[1]^[2]^[3] This intermediate metamorphic grade places phyllite between slate (lower grade, duller appearance) and schist (higher grade, coarser visible minerals), with its "crinkly" or wavy foliation arising from the slight deformation and growth of platy minerals during this process.^[4]^[1] In terms of composition, phyllite primarily consists of fine-grained quartz, chlorite, and sericite (a fine form of mica), often appearing in dark gray to black hues, though colors can vary to green or reddish depending on iron content.^[4] Its physical properties include a well-developed slaty cleavage that allows it to split into thin, flexible sheets, though the surfaces are shinier and more undulating than those of slate due to the larger (yet still microscopic) mica flakes.^[2] Unlike slate's perfectly flat breaks or schist's prominent mineral alignment, phyllite's texture provides moderate durability but can make it prone to weathering in exposed settings.^[1] Phyllite occurs widely in mountain belts and orogenic zones worldwide, such as the Green Mountains of Vermont, where it is part of formations like the Silurian-Devonian Waits River Formation, dating back 415–390 million years.^[4] In practical applications, it is quarried in regions like Loudoun County, Virginia, for use as roadstone and aggregate in construction, though its foliated nature limits it to lower-load applications compared to more isotropic rocks.^[5] Additionally, phyllite's fine-grained structure makes it relevant in geotechnical engineering, such as in tunneling and slope stability assessments, where its mechanical properties under dry or saturated conditions are studied for failure behavior.^[6]

Etymology

Origin of the term

The term "phyllite" originates from the Ancient Greek word φύλλον (phýllon), meaning "leaf," combined with the suffix -ite commonly used in mineralogical nomenclature to denote a rock type.^[7] This etymology reflects the rock's distinctive foliated texture, characterized by thin, leaf-like layering and cleavage planes that split into flexible sheets.^[8] The name evokes the visual resemblance of these aligned platy minerals to layered foliage, particularly evident in the rock's wavy, undulating surfaces. Phyllite's foliation, a key textural feature, arises from metamorphic alignment of fine-grained minerals, further underscoring the "leaf" analogy through its sheet-like parting.^[9] The visible silky sheen on cleavage surfaces, produced by minute mica crystals, enhances this leaf-like appearance by imparting a subtle luster akin to the glossy texture of certain leaves.^[9] In English, the term is pronounced /ˈfɪlaɪt/ (FIL-yite).^[7]

Historical usage

The term "phyllite" was first introduced by the German geologist Carl Friedrich Naumann in 1849 within the first edition of his Lehrbuch der Geognosie, where he defined it as a compact, lustrous schistose rock in which fine-grained sericite dominates the foliation, producing a structure intermediate between slate and more crystalline schists.^[10] This usage marked a refinement in describing low-grade metamorphic rocks with subtle sheen and fissility, building on Naumann's broader contributions to geognosie (historical geology). The concept evolved from earlier terms for foliated rocks, notably the French "phyllade," which Alexandre Brongniart introduced in 1813 in his Essai d'une classification des roches mélangées as a mixed thonschiefer-like rock exhibiting a feuilletée (foliated) texture with mica, quartz, felspar, and other minerals, positioned between slate and mica-schist in metamorphic gradation.^[11] Naumann's "phyllite" served as a Germanic variant, adapting and standardizing the nomenclature for such intermediate rocks in continental European texts during the mid-19th century. By the 1850s and 1860s, it gained traction in multilingual geological discourse, reflecting the era's emphasis on precise textural descriptions amid advancing stratigraphic mapping.^[10] Formalization in English occurred by the mid-19th century, with the term appearing in British and American publications as translations and adaptations of continental works; for instance, it was discussed in the Geological Magazine in 1867 as a distinct category for lustrous, fine-grained slates transitional to schists.^[11] This adoption aligned with the growing influence of petrographic microscopy and regional surveys, such as those by the Geological Survey of Great Britain. In 19th- and 20th-century petrology, "phyllite" significantly shaped classification systems by establishing a clear intermediate grade in the metamorphic spectrum, distinguishing it from slate—characterized by aphanitic texture and perfect slaty cleavage without sheen—and schist, with its coarser, visibly crystalline foliation and stronger mineral alignment. This differentiation, emphasized in works like Arthur Holmes's The Nomenclature of Petrology (1920), facilitated zonal mapping of metamorphic terrains and influenced seminal schemes, such as Ulrich Grubenmann's depth-based zonation (1910s), where phyllite occupied the upper low-grade zone under moderate temperature and stress conditions.

Description

Texture and structure

Phyllite exhibits a distinct foliated texture characterized by the preferred orientation of fine-grained platy minerals, primarily mica flakes, which align parallel to form pervasive cleavage planes. This alignment develops during low- to medium-grade metamorphism, imparting a planar fabric that defines the rock's overall structure at both microscopic and hand-sample scales. The foliation surfaces often display a satiny or silky sheen due to light reflection off these aligned mica crystals, and they frequently appear wavy or crenulated as a result of minor deformation or differential recrystallization.^[12]^[1] The grain size in phyllite is intermediate between that of slate and schist, with mica flakes typically ranging from 0.1 to 0.5 mm in length, making them barely visible to the naked eye but sufficient to produce the characteristic luster without forming the coarser, hand-visible crystals of schist. Non-platy minerals, such as quartz, remain fine-grained and interlocked within the matrix, contributing to a compact yet anisotropic fabric. This intermediate granularity arises from progressive metamorphic recrystallization of a finer-grained protolith, where clay minerals transform into oriented micas without achieving the pronounced segregation seen in higher-grade rocks.^[13]^[14] Phyllite demonstrates good fissility, allowing it to split into thin, flexible sheets along its foliation planes, though this cleavage is less perfect and more undulating than in slate due to the larger mica grains and subtle folding of the fabric. The role of mica minerals is central to this texture, as their platy habit and alignment control the rock's ability to fracture preferentially while imparting the wavy surfaces that distinguish it from smoother slates. These structural features make phyllite identifiable in hand samples by its crinkled, reflective layers.^[15]^[1]

Mineral composition

Phyllite is predominantly composed of fine-grained quartz, sericite (a variety of muscovite mica), and chlorite as its essential minerals.^[16]^[17] Quartz typically occurs as microcrystalline grains, while sericite and chlorite form the platy components that contribute to the rock's foliation.^[18] These minerals often constitute the bulk of the rock, with sericite comprising more than 50% in many examples.^[19] Accessory minerals in phyllite include biotite, which may appear in small amounts, and graphite, particularly in varieties derived from organic-rich protoliths, imparting a dark color and submetallic luster.^[18] In phyllites formed under contact metamorphic conditions, minerals such as andalusite or cordierite can occur as porphyroblasts.^[18] The mineral composition of phyllite varies depending on the protolith; for instance, those derived from iron-rich shales exhibit elevated chlorite content, resulting in greener hues and higher iron concentrations.^[20]^[8]

Properties

Physical properties

Phyllite possesses a hardness ranging from 3 to 3.5 on the Mohs scale, rendering it softer than quartz (Mohs 7) yet harder than talc (Mohs 1), which facilitates its identification through scratch tests with common tools like a copper penny or knife blade.^[21] This moderate hardness reflects the fine-grained matrix dominated by aligned mica flakes and quartz, allowing the rock to be scratched by a steel nail but resisting fingernail abrasion.^[22] The density of phyllite typically falls between 2.7 and 2.9 g/cm³, a value influenced primarily by its variable mica content, which can lower the overall specific gravity compared to more quartz-rich metamorphic rocks.^[23] Higher mica proportions contribute to slightly reduced density due to the mineral's lower specific gravity (around 2.8 g/cm³ for muscovite), while quartz inclusions (specific gravity 2.65 g/cm³) exert a balancing effect.^[24] This density range makes phyllite relatively lightweight for a metamorphic rock, aiding its use in applications requiring manageable weight without excessive fragility. In terms of appearance and breakage, phyllite commonly exhibits color variations of gray, black, or greenish-gray, arising from iron-bearing minerals and organic impurities in the protolith.^[16] Its fracture is uneven to conchoidal, with the foliation planes promoting sheet-like splitting (fissility) parallel to bedding, while perpendicular breaks display irregular or curved surfaces due to the interlocking of platy minerals.^[25] Regarding durability, phyllite demonstrates moderate resistance to weathering under dry conditions but is susceptible to delamination and softening in moist environments, where water infiltration along foliation planes accelerates mechanical breakdown and reduces structural integrity. This vulnerability stems from the expansive nature of clay minerals derived from mica alteration, leading to potential instability in engineering contexts like slope stability or construction aggregates.^[26]

Optical properties

Phyllite displays a characteristic phyllitic luster, manifesting as a silky to satiny sheen on its cleavage surfaces, which arises from the parallel alignment of fine-grained mica platelets such as muscovite or sericite.^[1]^[25] This reflective quality is enhanced by the minute size of the micas, which scatter light in a way that produces the distinctive glimmer, distinguishing phyllite from less lustrous rocks like slate. In varieties containing biotite, the sheen may take on a warmer, sometimes golden tone due to the mineral's brownish hues.^[18] Under microscopic examination in thin section, phyllite reveals additional optical traits under cross-polarized light. Quartz grains often exhibit undulose extinction, a wavy pattern resulting from crystal lattice deformation during metamorphism, while the micas show pronounced birefringence, producing vibrant interference colors that highlight their oriented fabric.^[27]^[28] These features underscore the rock's low- to medium-grade metamorphic history and the role of fine-grained micas in its overall texture. In hand samples, phyllite's semi-translucency in thin slabs facilitates identification, as light transmission through the fine-grained matrix reveals subtle internal structures and aids in confirming the presence of aligned platy minerals.^[25] This property, combined with the surface sheen, makes phyllite readily distinguishable in field settings.

Formation

Protolith

The protolith of phyllite is typically a fine-grained, clay-rich sedimentary rock such as shale, mudstone, or pelite.^[1]^[29] These protoliths consist predominantly of particles smaller than 0.06 mm, dominated by clay minerals that impart a high alumina content and plasticity to the sediment.^[30] Key characteristics of these protoliths include a high proportion of clay minerals like illite and kaolinite, which form through weathering processes and constitute over 60% of the rock's volume.^[30] Illite, derived from feldspar alteration or diagenetic changes in smectite, is especially prevalent in older mudrocks, while kaolinite indicates deposition in humid, leaching environments.^[30] During subsequent low-grade metamorphism, these clays recrystallize into fine-grained micas, contributing to phyllite's foliated texture.^[1] Less commonly, phyllite develops from volcanic protoliths such as ash or tuff, particularly in meta-volcanic settings where fine pyroclastic material mimics the clay-rich composition of sedimentary pelites.^[31]^[32]

Metamorphic conditions

Phyllite develops under regional metamorphism within the greenschist facies, where temperatures typically range from 300 to 450°C and pressures from 2 to 10 kbar.^[3]^[33] These conditions represent a low- to medium-grade metamorphic environment, intermediate between those forming slate and schist, and occur in convergent tectonic settings where burial and tectonic forces recrystallize the rock without melting.^[1] The primary process is progressive recrystallization of clay minerals in the protolith—commonly shale—into fine-grained white micas such as sericite and chlorite, along with quartz.^[12] This transformation involves the breakdown of detrital clays like kaolinite or illite, which reorganize into aligned platy crystals through solid-state diffusion and reactions facilitated by chemically active fluids containing water and ions.^[34] The fluids enhance mineral replacement by promoting metasomatism, where elements like potassium are introduced, converting kaolinite to sericite without significant volume change.^[34] Directed stress under these conditions induces a strong preferred orientation of the newly formed micas, developing slaty cleavage that evolves into the characteristic foliation of phyllite, marked by a silky sheen but lacking the coarse alignment of schistosity.^[12] The foliation planes form perpendicular to the maximum compressive stress, reflecting tectonic deformation that aligns sheet silicates while preserving the fine grain size due to the relatively moderate temperatures and pressures.^[1]

Occurrence

Geological settings

Phyllite commonly forms within orogenic belts, particularly along subduction zones and continental collision margins, where tectonic forces drive regional metamorphism of sedimentary protoliths during mountain-building episodes. These settings involve the convergence of tectonic plates, leading to crustal thickening and elevated pressures and temperatures that transform shales and mudstones into phyllite as an intermediate stage between slate and schist. For instance, in the Appalachian orogen, phyllites are prevalent in metasedimentary sequences deformed during Paleozoic collisional events, reflecting low-grade metamorphic overprints on earlier sedimentary layers. Similarly, in the Alpine orogen, phyllites appear in nappe structures and accretionary complexes, such as the Phyllite-Quartzite Unit, associated with Mesozoic-Cenozoic subduction and collision dynamics that exhumed these rocks along thrust faults.^[35]^[36]^[37] In addition to tectonic convergence, phyllite can develop through burial metamorphism in sedimentary basins, where accumulating overburden from overlying sediments or volcanic piles induces low-grade metamorphic conditions without intense deformation. This process often transitions into broader regional metamorphism as basins are incorporated into orogenic systems, subjecting the rocks to increasing heat and pressure gradients. Such environments are typical in foreland basins adjacent to evolving mountain belts, where pelitic sediments undergo progressive recrystallization while retaining fine-grained foliation.^[12]^[38]^[39] Phyllite frequently occurs interlayered with slate and quartzite within greenschist facies sequences, forming part of stacked metasedimentary units that record polyphase deformation in these tectonic contexts. These associations highlight phyllite's role in low-grade metamorphic piles, where it marks a transitional zone between less altered slates and more schistose rocks, often in response to the same greenschist facies conditions of moderate temperature and pressure.^[15]^[17]^[40]

Notable localities

Phyllite is prominently exposed in the Dalradian Supergroup of the Scottish Highlands, where it forms part of the variably metamorphosed metasedimentary sequence, including in northwest Arran as fine-grained, foliated rocks derived from original shales and mudstones.^[41] In north Cornwall, the Tredorn Phyllites represent a sequence of slates tentatively correlated with the overlying Woolgarden Phyllites, both part of the Upper Devonian Tredorn Slate Formation, featuring interlaminated slate and siltstone with rust-spotting from pyrite and low-grade metamorphic spotting near the Bodmin granite aureole.^[42]^[43] Along the Welsh borders, phyllite occurs in steeply inclined, fine-grained recrystallized schists of the Monian Supergroup, marking zones of regional metamorphism.^[44] In the United States, phyllite is widespread in the Carolina Slate Belt, a volcanic-dominated terrane in North Carolina, exemplified by the Duke stone—a fractured, iron oxide-colored dacitic phyllite quarried from metavolcanic argillite, tuff, and breccia for architectural dimension stone in over 100 buildings.^[45]^[46] Economic deposits are commercially extracted from active quarries in the Waits River Formation of east-central Vermont, where large quantities of this Silurian-Devonian phyllite serve as dimension stone for construction and landscaping.^[4] Globally, minor but geochemically significant occurrences of phyllite are documented in the Indian Himalayas, including the Patharkhola section of the Lesser Kumaun Himalaya, where it exhibits tectonic provenance from recycled sedimentary and volcanic sources, and the Chandpur Formation in Uttarakhand, which weathers into saprolitic soils.^[47]^[48]

Distinction from similar rocks

Comparison with slate

Phyllite and slate are both low-grade foliated metamorphic rocks derived primarily from clay-rich protoliths like shale, but they differ in texture, mineral development, and formation conditions, with phyllite representing a higher metamorphic grade.^[1] Slate features extremely fine-grained minerals too small to see with the naked eye, resulting in a dense, uniform structure, whereas phyllite exhibits slightly coarser micas that are not individually visible but impart a distinctive silky or satiny sheen to the rock's surfaces.^[49]^[2] In terms of foliation, slate displays perfect planar slaty cleavage, allowing it to split into thin, flat sheets with a dull, earthy luster, while phyllite shows a more wavy or crenulated foliation due to the alignment of recrystallized platy minerals like muscovite and chlorite, producing a subtle micaceous glimmer rather than sharp planar breaks.^[1]^[2] These textural differences arise from the progression in metamorphic grade: slate forms under sub-greenschist to low-grade conditions at temperatures of 150–300°C and low pressures, whereas phyllite develops in the greenschist facies at 200–320°C and moderate pressures, enabling greater mineral recrystallization.^[49] In the field, slate is readily identified by its ability to split into flatter, more regular slabs that produce a sharp, clanky sound when struck, whereas phyllite is distinguished by its less even splitting along undulating planes and the faint reflective sheen from oriented micas, which catches light at an angle.^[2]^[25] Phyllite occupies an intermediate position in the sequence of foliated metamorphic rocks from slate to higher-grade varieties.^[1]

Comparison with schist

Phyllite and schist represent distinct stages in the metamorphic progression of pelitic rocks, with schist exhibiting coarser grain sizes allowing visible mica flakes that define a well-developed schistosity often accompanied by mineral lineation.^[50] In contrast, phyllite features finer crystals, where mica minerals are not individually discernible but impart a subtle sheen to the foliation surfaces, resulting in less aligned and more uniform textures.^[49] This textural difference arises from the limited crystal growth in phyllite, preserving a finer-grained matrix compared to the pronounced flaky cleavage in schist, where micas like muscovite or biotite dominate visibly.^[1] Metamorphic grade further delineates these rocks, with phyllite forming under greenschist facies conditions at temperatures of approximately 200–320°C and moderate pressures, fostering recrystallization without extensive coarsening.^[51] Schist, however, develops at higher amphibolite facies grades, exceeding 450°C and often reaching up to 700°C, enabling significant mineral growth and reorientation that enhance schistosity.^[52] These elevated conditions in schist promote the stability of index minerals such as garnet or staurolite, absent or minimal in phyllite, underscoring the thermal boundary between the two.^[53] The transition from phyllite to schist occurs gradually with increasing heat and pressure, where the fine-grained uniformity of phyllite gives way to coarser, aligned crystals as metamorphic intensity rises, marking the boundary in regional metamorphism sequences.^[2] This progression reflects enhanced diffusion and recrystallization, transforming the subtle phyllitic sheen into the prominent, peelable layers characteristic of schist.^[54]

Uses

Construction and decoration

Phyllite is widely employed as a dimension stone in construction due to its durability and ability to be cut into thin, uniform slabs. It serves as facing stone for building exteriors, providing a resilient veneer that withstands environmental exposure while contributing to architectural aesthetics. Additionally, phyllite is used for curbing and paving slabs, where its resistance to weathering and mechanical stress ensures longevity in outdoor applications, particularly in temperate climates.^[55]^[56] In decorative contexts, phyllite's fine-grained foliation allows it to be polished to reveal wavy patterns and a subtle sheen, enhancing its visual appeal for interior and exterior ornamentation. Common applications include countertops and floor tiles in homes and public spaces, where the stone's polishability and low porosity resist stains and wear. It is also utilized for garden ornaments and cemetery markers, offering both functional durability and an elegant, natural texture that complements landscaping and memorials.^[55]^[57] The stone's advantages in these uses stem from its low metamorphic grade, which imparts good fissility for controlled splitting into slabs without excessive fracturing, combined with inherent weather resistance that prevents degradation from moisture and temperature fluctuations. This makes phyllite a preferred choice over more brittle alternatives in regions with moderate seasonal changes, balancing structural integrity with ornamental qualities.^[56]^[55]

Other applications

Historically, phyllite has been utilized as an alternative to slate for writing slates and blackboards, owing to its smooth cleavage surfaces that allow for easy writing and erasure with chalk or slate pencils.^[16] Phyllite's fine-grained texture provided a durable yet writable medium for students and educators.^[58] In industrial contexts, phyllite serves as an aggregate in concrete, leveraging its pozzolanic properties derived from fine silicate minerals like quartz and mica, which react with calcium hydroxide to enhance long-term strength and durability when calcined.^[59] Studies show that substituting up to 10-20% Portland cement with calcined phyllite maintains compressive strengths comparable to control mixes, reducing environmental impact by lowering clinker demand.^[60] Additionally, phyllite clays are employed in ceramics production, where firing at 1100-1200°C yields low-porosity vitrified materials suitable for tiles and sanitary ware, with chemical compositions rich in SiO₂ and Al₂O₃ contributing to thermal stability.^[61] As of 2024, phyllite is increasingly used as a sustainable resource in regions like Ghana for mining and recycled aggregates in construction, supporting economic development and waste reduction.^[62]^[63] Artistically, phyllite's subtle sheen and color variations—often in shades of gray, green, or purple—make it a favored material for sculptures, as seen in ancient Indian Pala-style figures carved from chloritoid phyllite, which allows intricate detailing while resisting weathering.^[64] In modern landscaping, phyllite is incorporated into decorative elements like garden paving and ornamental features, where its foliated structure adds textural contrast and durability to outdoor designs.^[65]

References

[1]
Metamorphic Rocks - Tulane University
Sep 25, 2017 · Phyllite - Fine mica-rich rock, formed by low – medium grade metamorphism. In a phyllite, the clay minerals have recrystallized into tiny ...
[2]
Metamorphic Rocks – Introduction to Earth Science
Phyllite is a foliated metamorphic rock in which platy minerals have grown larger and the surface of the foliation shows a sheen from light reflecting from the ...
[3]
Vermont State Rocks | Department of Environmental Conservation
The phyllite is a metamorphic rock that formed at thermodynamic (temperature and pressure) conditions intermediate between those that produce slate (low ...Missing: properties | Show results with:properties
[4]
Virginia Energy - Geology and Mineral Resources - Loudoun County
Basalt, diabase, gneiss, phyllite, pyroclastic rock, and conglomerate have been quarried for use as roadstone, and locally as road metal. Some of the companies ...
[5]
Mechanical Properties and Failure Behavior of Dry and Water ...
Dec 15, 2022 · As a typical metamorphic rock, phyllite is encountered frequently in mining and geotechnical engineering, e.g., in tunneling, underground ...
[6]
phyllite, n. meanings, etymology and more | Oxford English Dictionary
phyllite is a borrowing from Greek, combined with an English element. Etymons: Greek ϕύλλον, ‑ite suffix1. See etymology ...
[7]
Phyllite Definition, Formation & Composition - Study.com
The name originated from the Greek word phyllon, which means "leaf," indicating phyllite's characteristic thin and sheet-like cleavage. Sheet-like ...Missing: called | Show results with:called
[8]
Overview of Phyllite - ThoughtCo
Feb 28, 2019 · Phyllite owes its silky sheen to microscopic crystals of white mica the variety called sericite, which is used in cosmetics for a similar effect ...
[9]
[PDF] 601 Faurteenth list of new mineral names. 1 By L. J. SPENCER ...
Phyllite (C. F. Naumann, 1849), a variant of the French phyllade (A. Brongniart, 1813), is in common use for a slaty-schistose.
[10]
VIII.—Phyllade, Phyllite, and Ottrelite | Geological Magazine
May 1, 2009 · He says that the surface of phyllade is sometimes smooth, sometimes deeply striated, as if puckered up (“froncée”); and he shows how the true ...
[11]
6 Metamorphic Rocks – An Introduction to Geology - OpenGeology
Each rock name has a specific texture that defines and distinguishes it. The most important of these are slate, phyllite, schist and gneiss, described below.
[12]
Cement improved highly weathered phyllite for highway subgrades
... grain size 0.1–0.4 mm. The ... Existing research (Shu, 2008) suggests that the amount and the structure of mica affect the strength of the phyllite.
[13]
https://www.sciencedirect.com/science/article/pii/S2095756417303094
[14]
[PDF] METAMORPHIC ROCKS, PART 1 LOWER-GRADE REGIONAL ...
Mar 14, 2012 · Phyllites often exhibit corrugated cleavage surfaces. Spotted phyllites are bumpy due to the formation of incipient porphyroblasts. Greenstone ...
[15]
Phyllite - an overview | ScienceDirect Topics
The phyllite forms from pelitic sediments (shale and mudstone) at a slightly higher degree of regional metamorphism from slate (Table 7.1). It may also ...Missing: etymology | Show results with:etymology
[16]
Phyllite - ALEX STREKEISEN
The term (from the Greek phyllos, leaf, a reference to its characteristic cleavage) was first used by C. F. Naumann in the late 1850s, but the original ...Missing: etymology | Show results with:etymology
[17]
Phyllite: Metamorphic Rock - Pictures, Definition & More
Phyllite is a foliated metamorphic rock that forms under low levels of heat and pressure. It is composed of fine-grained sheet silicate minerals.Missing: etymology | Show results with:etymology<|control11|><|separator|>
[18]
Phyllit
Phyllite is formed from clay shale during regional metamorphism. Compared to clay shale, which still belongs to the sedimentary rocks, phyllite has no ...Missing: Naumann 1849
[19]
Phyllite | Geology 1501 | ECU
Type, Metamorphic Rock ; Texture, Foliated; Fine-grained ; Composition, Muscovite, Biotite, Quartz, Plagioclase ; Index Minerals ; Color, Shiny Gray.Missing: structure | Show results with:structure
[20]
[PDF] SAMPLE DESCRIPTION - INSTAP Study Center for East Crete
Please observe: Mohs hardness refers to minerals only, not a rock per se (as ... ECl. ~LE. Type: metamorphic rock; intercalated between purple phyllite.
[21]
Otta Rust - Gold Phyllite - StoneContact.com
On the Mohs scale of mineral hardness, phyllite typically falls within the range of 2.5 to 3.5. Nevertheless, as the hardness of a rock can vary based on ...
[22]
Phyllite vs. slate: differences and characteristics - Cupa Pizarras
So, slates and phyllites have common properties. They are only differentiated by the higher metamorphic grade of the phyllites. However, this small increase in ...
[23]
Properties of Phyllite | Physical | Thermal - Compare Rocks
The hardness of Phyllite is 1-2 whereas its compressive strength is 50.00 N/mm2. Streak is the color of rock when it is crushed or powdered. The streak of ...
[24]
7.5 Metamorphic Rock Field Guide - Maricopa Open Digital Press
Phyllite is fine-grained and composed mostly of quartz, feldspar, and visible flakes of mica minerals. These enlarged mica crystals give phyllite a shimmering ...
[25]
Physical and geotechnical properties of clay phyllites - ResearchGate
Aug 5, 2025 · The ductility, flexural strength and shear strength of phyllite RC beams got decreased as compared to conventional aggregate beams [5]. Phyllite ...
[26]
KGS--Petrography of Upper Permian Rocks--Mineralogy
Aug 25, 2006 · ... undulose extinction. Nearly all the large rounded quartz grains show ... Rare phyllite and fine-grained schist occur in sandstones in several ...
[27]
Phyllite Thin Section in Polarized Light - Molecular Expressions
An examination of geological thin sections of the mineral phyllite using polarizing microscopy, as well as providing information on component minerals.Missing: properties luster translucency
[28]
Low Grade Metamorphism - an overview | ScienceDirect Topics
Phyllite forms from pelitic sediments (shale and mudstone) at slightly higher degree of regional metamorphism from slate (Table 6.1). It may also result ...<|control11|><|separator|>
[29]
Mudrocks
Apr 17, 2013 · The fine grain size of these sediments means that that the sediment can be suspended for long times in relatively quiet, low energy currents.
[30]
10 Different Kinds of Metamorphic Rocks – Open Petrology
... mica and chlorite grains are coarser in phyllite than in slate. Phyllitic luster – which is absent from slate and schist – really defines a phyllite.
[31]
Mona Formation
Its protolith was likely a volcanic tuff. Mona Formation chlorite-sericite-quartz phyllite (field of view ~7.7 cm across) from ...
[32]
7.2 Classification of Metamorphic Rocks – Physical Geology
Phyllite is similar to slate, but has typically been heated to a higher temperature; the micas have grown larger and are visible as a sheen on the surface.
[33]
Greenschist Facies - an overview | ScienceDirect Topics
Greenschist facies refers to a metamorphic condition characterized by temperatures of approximately 400–550 °C and pressures between 2–10 kbar, typically ...
[34]
The transformation of clay minerals during diagenesis and low ...
Aug 7, 2025 · 6A, B). Illitization of kaolinite is a common clay transformation during burial diagenesis and low-grade metamorphism (Dunoyer de Segonzac 1970 ...
[35]
Margarite-corundum phyllites from the Appalachian orogen of South ...
Mar 9, 2017 · Margarite and corundum are by far the most abundant phases in these phyllites, constituting >95% of each of the samples investigated. Minor ...
[36]
Rocks of the Appalachians and Piedmont - Earth@Home
Sep 28, 2023 · These rocks were metamorphosed to slate, phyllite, and quartzite during later orogenic events, and they are often referred to as " ...Missing: Alps | Show results with:Alps
[37]
Nappe Imbrication Within the Phyllite‐Quartzite Unit of West Crete ...
Oct 19, 2022 · We studied a well-known nappe of high-pressure metamorphic rocks (the Phyllite-Quartzite Unit) on the island of Crete in Greece, which was ...
[38]
6.5: Metamorphic Environments - Geosciences LibreTexts
Aug 25, 2025 · Burial metamorphism commonly occurs in sedimentary basins, where rocks are buried deeply by overlying sediments.
[39]
[PDF] Types of Metamorphism
• Spotted phyllite (or slate) ... regional contact metamorphism. Orogenic Metamorphism. Burial Metamorphism. • Low -grade metamorphism in sedimentary basins.
[40]
[PDF] Quartzite sequences and their relationships, Woodburn Lake group ...
The quartzite is interlayered and interfolded with pyritic quartz-pebble conglomerate (Fig. 6f), phyllite, chloritoid-kyanite slate, and quartz-feldspar por-.
[41]
Geological History of Arran | Isle of Arran Heritage Museum
The Dalradian rocks found on Arran were deposited on the bottom of a deep Ocean as sedimentary rocks such as greywackes , black muds and shales. They were laid ...
[42]
The Upper Devonian and Lower Carboniferous Stratigraphy of Boscastle and Tintagel, Cornwall | Geological Magazine | Cambridge Core
### Summary of Tredorn Phyllites in Cornwall
[43]
BGS Lexicon of Named Rock Units - Result Details
Slate and siltstone are interlaminated in places; within the aureole of the Bodmin granite this gave rise to distinctively banded slates ('Woolgarden Phyllites ...
[44]
Wales: British regional geology - BGS Application Server
Most of the rocks within the zone are steeply inclined, fine-grained, recrystallised schist and phyllite; both margins are gradational. Monian Supergroup. The ...
[45]
[PDF] geology and mineral resources of orange county, north carolina | nc ...
Butler (1964) states, "The Duke quarly phyllite was derived fi·om argillite, tuff or tuffaceous sandstone, and volcanic breccia. Occurrence of laminated argil-.
[46]
Take A Walk In The 'Local' Woods: Duke Forest, Trees, Mushrooms ...
Nov 4, 2016 · ... stone for Duke's West Campus buildings. The 400 million year old metamorphic volcanic rock (phyllite of the Carolina Slate Belt) in this ...
[47]
[PDF] Petrochemistry of Phyllites from Patharkhola, Lesser Kumaun ...
Jul 21, 2023 · Phyllites from Patharkhola, Lesser Kumaun Himalaya have been studied to investigate the geochemical characteristics of these rocks and their ...
[48]
Geotechnical and micro-structural characteristics of phyllite derived ...
The Chandpur Formation, in Uttarakhand (India), contains different varieties of phyllites. At places, it has decomposed into regolitic/saprolitic soil mass, ...
[49]
7.2 Classification of Metamorphic Rocks – Physical Geology
Phyllite is similar to slate, but has typically been heated to a higher temperature; the micas have grown larger and are visible as a sheen on the surface.
[50]
Classification of Metamorphic Rocks
In order of increasing grain size, foliated textures are referred to as SLATY (aphanitic, very fine-grained), PHYLLITIC (aphanitic, fine-grained), SCHISTOSE ( ...Missing: structure | Show results with:structure
[51]
Types of Metamorphism
Apr 12, 2018 · Low-grade metamorphism takes place at temperatures between about 200 to 320oC, and relatively low pressure. Low grade metamorphic rocks are ...
[52]
Metamorphic Rocks Lesson #14 | Volcano World
Schist is a medium grade metamorphic rock. This means that it has been subjected to more heat and pressure than slate, which is a low grade metamorphic rock.
[53]
Metamorphic Rocks
Schist and gneiss are produced by medium to high grade metamorphism. In some cases gneisses are produced by higher grade metamorphism than schists. Low-grade ...
[54]
Classification of Metamorphic Rocks
Phyllite is intermediate between slate and schist. It differs from slate in that crystallization of micaeous minerals imparts a sheen to the rock; it differs ...
[55]
Phyllite | Composition, Properties, Formation, Uses - Geology Science
Apr 13, 2019 · Name origin: The term of phyllite comes from the Greek phyllon, meaning “leaf”. Protolith or Parent Rock: Parent rock for phyllite is shale or ...Missing: etymology | Show results with:etymology
[56]
THE BERNARDOS PHYLLITE RECOGNIZED WORLD HERITAGE ...
Today the production of the Naturpiedra quarry in Bernardos has diversified into paving, flagstones, coatings, kerbs, Japanese steps, decorative rocks, and many ...<|control11|><|separator|>
[57]
Metamorphic Rocks Gallery
Anthracite will fracture leaving uneven broken surfaces and has a submetallic luster giving it a shiny appearance. ... Phyllite. Phylite. PreviousNext. 1; 2; 3.
[58]
https://www.sciencedirect.com/science/article/pii/B9780128205853000077
[59]
Sericitic Phyllite as Addition in Portland Cement - ResearchGate
Apr 24, 2025 · The present work evaluated the possibility of the Sericitic Phyllite acquires pozzolanic properties from thermal treatment, to be used as ...
[60]
[PDF] 26 Evaluating Shale, Slate, Phyllite and Volcanic Ash as Natural ...
Abstract: The role of natural pozzolanas is considered to be important especially when the concrete is subjected to acidic, alkaline, saline or waterlogged ...
[61]
Characterization, thermal and ceramic properties of phyllite clays ...
Aug 10, 2020 · According to the present results, the phyllite clays have potential applications as ceramic raw materials of wide interest.
[62]
Stone and the Production of Images - jstor
The rock that the sculptors most commonly used is best and most accurately described as chloritoid phyllite. Sculptures from other parts of Bihar, especially ...
[63]
Buy Phyllite Stone with unique finishes
Being a hard and durable stone, Phyllite can be used for flooring, wall cladding in both interiors and exteriors, paving, landscaping, swimming pools and ...