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55-495: The original structure is a 2 + 1 ⁄ 2 -story, five-bay brick house, altered by the Van Cortlandt family in the 1830s. It has a gable roof covered in slate . A large 2 + 1 ⁄ 2 -story frame wing covered in stucco was built in the 1920s. It was built or remodeled in 1773 by Pierre Van Cortlandt . After 1783, the house was occupied by his son Pierre Van Cortlandt, Jr. (1762–1848) until his death. In 1889,

110-614: A pelite . Slate can be made into roofing slate, a type of roof tile which are installed by a slater . Slate has two lines of breakability—cleavage and grain—which make it possible to split the stone into thin sheets. When broken, slate retains a natural appearance while remaining relatively flat and easy to stack. A series of "slate booms" occurred in Europe from the 1870s until the First World War following improvements in railway, road and waterway transportation systems. Slate

165-472: A P-T-t (pressure, temperature, time) path for a rock, as the relationship of a foliation to porphyroblasts is diagnostic of when the foliation formed, and the P-T conditions which existed at that time. Linear structures in a rock may arise from the intersection of two foliations or planar structures, such as a sedimentary bedding plane and a tectonically induced cleavage plane. The degree of lineation compared with

220-462: A background mass made of much finer grains. Fragmental textures include clastic , bioclastic , and pyroclastic . A preferred mineral orientation , is the texture of metamorphic rock in which its grains have a flattened shape (inequant), and their planes tend to be oriented in the same direction. Rock microstructure includes the texture and small-scale structures of a rock . The words texture and microstructure are interchangeable, with

275-643: A binocular microscope, not in a thin section . Composition of the clasts can give clues as to the derivation of a rock's sediments. For instance, volcanic fragments, fragments of cherts, well-rounded sands all imply different sources. The matrix of a sedimentary rock and the mineral cement (if any) holding it together are all diagnostic. Usually diagenesis results in a weak bedding-plane foliation . Other effects can include flattening of grains, pressure dissolution and sub-grain deformation. Mineralogical changes may include zeolite or other authigenic minerals forming in low-grade metamorphic conditions. Sorting

330-453: A light-green, spotted texture. These spheres are sometimes deformed by a subsequent applied stress field into ovoids, which appear as ellipses when viewed on a cleavage plane of the specimen. However, some evidence shows that reduced spots may also form after deformation and acquire an elliptical shape from preferential infiltration along the cleavage direction, so caution is required in using reduction ellipsoids to estimate deformation. Before

385-406: A long-lasting weathertight roof with a lifespan of around 60–125 years. Some mainland European slate suppliers suggest that using hook fixing means that: The metal hooks are, however, visible and may be unsuitable for historic properties. Slate tiles are often used for interior and exterior flooring, stairs, walkways and wall cladding. Tiles are installed and set on mortar and grouted along

440-410: A loss of up to 50% of the volume of the mudrock as it is compacted. Grains of platy minerals, such as clay minerals , are rotated to form parallel layers perpendicular to the direction of compaction, which begin to impart cleavage to the rock. Slaty cleavage is fully developed as the clay minerals begin to be converted to chlorite and mica. Organic carbon in the rock is converted to graphite . Slate

495-439: A property called fissility , forming smooth, flat sheets of stone which have long been used for roofing , floor tiles, and other purposes. Slate is frequently grey in color, especially when seen en masse covering roofs. However, slate occurs in a variety of colors even from a single locality; for example, slate from North Wales can be found in many shades of grey, from pale to dark, and may also be purple, green, or cyan. Slate

550-570: A rudimentary damp-proof membrane . Small offcuts are used as shims to level floor joists. In areas where slate is plentiful it is also used in pieces of various sizes for building walls and hedges, sometimes combined with other kinds of stone. Because it is a good electrical insulator and fireproof, it was used to construct early-20th-century electric switchboards and relay controls for large electric motors . Because of its thermal stability and chemical inertness, slate has been used for laboratory bench tops and for billiard table tops. Slate

605-472: A time especially if it is cooling slowly. This is why most igneous rocks have only one type of phenocryst mineral. Rhythmic cumulate layers in ultramafic intrusions are a result of uninterrupted slow cooling. When a rock cools too quickly the liquid freezes into a solid glass, or crystalline groundmass. Often vapor loss from a magma chamber will cause a porphyritic texture. Embayments or 'corroded' margins to phenocrysts infer that they were being resorbed by

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660-421: A variety of ways, and interpretations of the intergrowths can be critical in understanding both magmatic and cooling histories of igneous rocks. A few of the many important textures are presented here as examples. Graphic , micrographic , and granophyric textures are examples of intergrowths formed during magmatic crystallization. They are angular intergrowths of quartz and alkali feldspar . When well-developed,

715-422: Is a fine-grained, metamorphic rock that shows no obvious compositional layering but can easily be split into thin slabs and plates. It is usually formed by low-grade regional metamorphism of mudrock . This mild degree of metamorphism produces a rock in which the individual mineral crystals remain microscopic in size, producing a characteristic slaty cleavage in which fresh cleavage surfaces appear dull. This

770-426: Is also an important factor in the texture of an igneous rock. Crystals may be euhedral, subeuhedral or anhedral: Rocks composed entirely of euhedral crystals are termed panidiomorphic , and rocks composed entirely of subhedral crystals are termed subidiomorphic . Porphyritic structure is caused by the nucleation of crystal sites and the growth of crystals in a liquid magma. Often a magma can only grow one mineral at

825-528: Is also fire resistant and energy efficient. Slate roof tiles are usually fixed (fastened) either with nails or with hooks (as is common with Spanish slate). In the UK, fixing is typically with double nails onto timber battens (England and Wales) or nailed directly onto timber sarking boards (Scotland and Northern Ireland). Nails were traditionally of copper, although there are modern alloy and stainless steel alternatives. Both these methods, if used properly, provide

880-443: Is an intergrowth of K-feldspar with albite feldspar, formed by exsolution from an alkali feldspar of intermediate composition: the coarseness of perthitic intergrowths is related to cooling rate. Perthite is typical of many granites . Myrmekite is a microscopic, vermicular (worm-like) intergrowth of quartz and sodium-rich plagioclase common in granite; myrmekite may form as alkali feldspar breaks down by exsolution and silicon

935-442: Is in contrast to the silky cleaved surfaces of phyllite , which is the next-higher grade of metamorphic rock derived from mudstone. The direction of cleavage is independent of any sedimentary structures in the original mudrock, reflecting instead the direction of regional compression. Slaty cleavage is continuous, meaning that the individual cleavage planes are too closely spaced to be discernible in hand samples. The texture of

990-494: Is listed on the National Register of Historic Places , is a stub . You can help Misplaced Pages by expanding it . Slate Slate is a fine-grained, foliated , homogeneous, metamorphic rock derived from an original shale -type sedimentary rock composed of clay or volcanic ash through low-grade, regional metamorphism . It is the finest-grained foliated metamorphic rock. Foliation may not correspond to

1045-462: Is mainly composed of the minerals quartz, illite , and chlorite, which account for up to 95% of its composition. The most important accessory minerals are iron oxides (such as hematite and magnetite ), iron sulfides (such as pyrite ), and carbonate minerals. Feldspar may be present as albite or, less commonly, orthoclase . Occasionally, as in the purple slates of North Wales , ferrous ( iron(II) ) reduction spheres form around iron nuclei, leaving

1100-486: Is not to be confused with shale, from which it may be formed, or schist . The word "slate" is also used for certain types of object made from slate rock. It may mean a single roofing tile made of slate, or a writing slate , which was traditionally a small, smooth piece of the rock, often framed in wood, used with chalk as a notepad or notice board, and especially for recording charges in pubs and inns. The phrases "clean slate" and " blank slate " come from this usage. Slate

1155-505: Is particularly suitable as a roofing material as it has an extremely low water absorption index of less than 0.4%, making the material resistant to frost damage. Natural slate, which requires only minimal processing, has an embodied energy that compares favorably with other roofing materials. Natural slate is used by building professionals as a result of its beauty and durability. Slate is incredibly durable and can last several hundred years, often with little or no maintenance. Natural slate

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1210-416: Is the result of cooling and nucleation of material in a magma which has achieved supersaturation in the crystal component. Thus it is often a subsolidus process in supercooler felsic rocks. Often, two minerals will grow together in the spherulite. Axiolitic texture results from spherulitic growth along fractures in volcanic glass, often from invasion of water. Intergrowths of two or more minerals can form in

1265-549: Is transported by fluids in cooling rocks. Iron-titanium oxides are extremely important, as they carry the predominant magnetic signatures of many rocks, and so they have played a major role in our understanding of plate tectonics . These oxides commonly have complex textures related both to exsolution and oxidation. For instance, ulvospinel in igneous rocks such as basalt and gabbro commonly oxidizes during subsolidus cooling to produce regular intergrowths of magnetite and ilmenite . The process can determine what magnetic record

1320-539: Is used to describe the uniformity of grain sizes within a sedimentary rock. Understanding sorting is critical to making inferences on the degree of maturity and length of transport of a sediment. Sediments become sorted on the basis of density, because of the energy of the transporting medium. High energy currents can carry larger fragments. As the energy decreases, heavier particles are deposited and lighter fragments continue to be transported. This results in sorting due to density. Sorting can be expressed mathematically by

1375-684: The Mid North at Mintaro and Spalding . Slate is abundant in Brazil , the world's second-largest producer of slate, around Papagaios in Minas Gerais , which extracts 95 percent of Brazil's slate. However, not all "slate" products from Brazil are entitled to bear the CE mark . Most slate in Europe today comes from Spain , the world's largest producer and exporter of natural slate, and 90 percent of Europe's natural slate used for roofing originates from

1430-668: The calls of all four species of wild turkey in North America: eastern, Rio Grande, Osceola and Merriam's. Slate is found in the Arctic and was used by Inuit to make the blades for ulus . China has vast slate deposits; in recent years its export of finished and unfinished slate has increased. Deposits of slate exist throughout Australia, with large reserves quarried in the Adelaide Hills in Willunga , Kanmantoo , and

1485-447: The component particles or crystals are referred to as the crystallographic texture or preferred orientation . Textures can be quantified in many ways. A common parameter is the crystal size distribution. This creates the physical appearance or character of a rock, such as grain size, shape, arrangement, and other properties, at both the visible and microscopic scale. Textures are penetrative fabrics of rocks; they occur throughout

1540-439: The conditions of formation, petrogenesis , and subsequent deformation, folding, or alteration events. Crystalline textures include phaneritic , foliated , and porphyritic . Phaneritic textures are where interlocking crystals of igneous rock are visible to the unaided eye. Foliated texture is where metamorphic rock is made of layers of materials. Porphyritic texture is one in which larger pieces ( phenocrysts ) are embedded in

1595-419: The degree of foliation for certain strain markers in deformed rocks are commonly plotted on a Flinn diagram. Very distinctive textures form as a consequence of ductile shear. The microstructures of ductile shear zones are S-planes, C-planes and C' planes. S-planes or schistosity planes are parallel with the shear direction and are generally defined by micas or platy minerals. Define the flattened long-axis of

1650-438: The development of foliation and overprinting of foliations causing crenulations . The relationship of porphyroblasts to the foliations and to other porphyroblasts can provide information on the order of formation of metamorphic assemblages or facies of minerals. Shear textures are particularly suited to analysis by microstructural investigations, especially in mylonites and other highly disturbed and deformed rocks. On

1705-634: The edges. Chemical sealants are often used on tiles to improve durability and appearance, increase stain resistance, reduce efflorescence , and increase or reduce surface smoothness. Tiles are often sold gauged, meaning that the back surface is ground for ease of installation. Slate flooring can be slippery when used in external locations subject to rain. Slate tiles were used in 19th century UK building construction (apart from roofs) and in slate quarrying areas such as Blaenau Ffestiniog and Bethesda , Wales there are still many buildings wholly constructed of slate. Slates can also be set into walls to provide

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1760-432: The entirety of the rock mass on microscopic, hand-sized specimen, and often outcrop scales. This is similar in many ways to foliations , except a texture does not necessarily carry structural information in terms of deformation events and orientation information. Structures occur on a hand-sized specimen scale and above. Microstructure analysis describes the textural features of the rock, and can provide information on

1815-503: The hand-sized specimen and outcrop scale. This is especially vital for describing phenocrysts and fragmental textures of tuffs , as often relationships between magma and phenocryst morphology are critical for analysing cooling, fractional crystallization and emplacement. Analysis of intrusive rock microstructures can provide information on source and genesis, including contamination of igneous rocks by wall rocks and identifying crystals which may have been accumulated or dropped out of

1870-608: The house was converted for use as a convalescent home and was later used as a nursing home . During the American Revolutionary War , the house served as headquarters for General George Washington from November 10 to 12, 1776; November 28 to 30, 1779; and June 25 to July 2, 1781. It was added to the National Register of Historic Places in 1981. This article about a historic property or district in Westchester County , New York , that

1925-409: The intergrowths may resemble ancient cuneiform writing, hence the name. These intergrowths are typical of pegmatite and granophyre , and they have been interpreted as documenting simultaneous crystallization of the intergrown minerals in the presence of a silicate melt together with a water-rich phase. Intergrowths that form by exsolution are aids in interpreting cooling histories of rocks. Perthite

1980-555: The late 19th and early 20th centuries, where the slate is usually dark purple to blackish, and many local structures are roofed with slate tiles. The roof of St. Patrick's Cathedral in New York City and the headstone of John F. Kennedy 's gravesite in Arlington National Cemetery are both made of Monson slate. Texture (geology) In geology , texture or rock microstructure refers to

2035-519: The latter preferred in modern geological literature. However, texture is still acceptable because it is a useful means of identifying the origin of rocks, how they formed, and their appearance. Description of sedimentary rock microstructure aims to provide information on the conditions of deposition of the sediment , the paleoenvironment , and the provenance of the sedimentary material. Methods involve description of clast size, sorting, composition, rounding or angularity, sphericity and description of

2090-495: The length of sediment transport . The more rounded the clasts, the more water or wind-worn they are. Particle shape includes form and rounding. Form indicates whether a grain is more equant (round, spherical) or platy (flat, disc-like, oblate); as well as sphericity. Roundness refers to the degree of sharpness of the corners and edges of a grain. The surface texture of grains may be polished, frosted, or marked by small pits and scratches. This information can usually be seen best under

2145-452: The liquid is well below the mineral growth curve. Growth then occurs at extreme rates, favoring slender, long crystals. Additionally, at crystal vertices and terminations, spikes and skeletal shapes may form because growth is favoured at crystal edges. Spinifex or dendritic texture is an example of this result. Hence, the shape of phenocrysts can provide valuable information on cooling rate and initial magma temperature. Spherulitic texture

2200-565: The magma and may imply addition of fresh, hotter magma. Ostwald ripening is also used to explain some porphyritic igneous textures, especially orthoclase megacrystic granites. A crystal growing in a magma adopts a habit (see crystallography ) which best reflects its environment and cooling rate. The usual phenocryst habit is the ones commonly observed. This may imply a 'normal' cooling rate. Abnormal cooling rates occur in supercooled magmas, particularly komatiite lavas. Here, low nucleation rates due to superfluidity prevent nucleation until

2255-488: The matrix. Sedimentary microstructures, specifically, may include microscopic analogs of larger sedimentary structural features such as cross-bedding , syn-sedimentary faults, sediment slumping, cross-stratification, etc. The maturity of a sediment is related not only to the sorting (mean grain size and deviations), but also to the fragment sphericity, rounding and composition. Quartz-only sands are more mature than arkose or greywacke . Fragment shape gives information on

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2310-440: The melt. This is especially critical for komatiite lavas and ultramafic intrusive rocks. Igneous microstructure is a combination of cooling rate, nucleation rate, eruption (if a lava ), magma composition and its relationships to what minerals will nucleate, as well as physical effects of wall rocks, contamination and especially vapor. According to the texture of the grains, igneous rocks may be classified as Crystal shape

2365-509: The mid-19th century, the terms "slate", " shale ", and " schist " were not sharply distinguished. In the context of underground coal mining in the United States, the term slate was commonly used to refer to shale well into the 20th century. For example, roof slate referred to shale above a coal seam , and draw slate referred to shale that fell from the mine roof as the coal was removed. The British Geological Survey recommends that

2420-417: The original sedimentary layering, but instead is in planes perpendicular to the direction of metamorphic compression. The foliation in slate, called " slaty cleavage ", is caused by strong compression in which fine-grained clay forms flakes to regrow in planes perpendicular to the compression. When expertly "cut" by striking parallel to the foliation with a specialized tool in the quarry, many slates display

2475-476: The relationship between the materials of which a rock is composed. The broadest textural classes are crystalline (in which the components are intergrown and interlocking crystals), fragmental (in which there is an accumulation of fragments by some physical process), aphanitic (in which crystals are not visible to the unaided eye), and glassy (in which the particles are too small to be seen and amorphously arranged ). The geometric aspects and relations amongst

2530-803: The slate from Wales and Cumbria is colored slate (non-blue): purple and formerly green in Wales and green in Cumbria. In North America, slate is produced in Newfoundland , eastern Pennsylvania , Buckingham County, Virginia , and the Slate Valley region in Vermont and New York , where colored slate is mined in the Granville, New York , area. A major slating operation existed in Monson, Maine , during

2585-753: The slate industry there. Lesser slate-producing regions in present-day Europe include Wales (with UNESCO landscape status and a museum at Llanberis ), Cornwall (famously the village of Delabole ), Cumbria (see Burlington Slate Quarries , Honister Slate Mine and Skiddaw Slate ) and, formerly in the West Highlands of Scotland, around Ballachulish and the Slate Islands in the United Kingdom . Parts of France ( Anjou , Loire Valley , Ardennes , Brittany , Savoie ) and Belgium (Ardennes), Liguria in northern Italy , especially between

2640-544: The slate is totally dominated by these pervasive cleavage planes. Under a microscope, the slate is found to consist of very thin lenses of quartz and feldspar (QF-domains) separated by layers of mica (M-domains). These are typically less than 100 μm (micron) thick. Because slate was formed in low heat and pressure, compared to most other metamorphic rocks, some fossils can be found in slate; sometimes even microscopic remains of delicate organisms can be found in slate. The process of conversion of mudrock to slate involves

2695-441: The standard deviation of the grain-size frequency curve of a sediment sample, expressed as values of φ (phi). Values range from <0.35φ (very well sorted) to >4.00φ (extremely poorly sorted). The study of metamorphic rock microstructures aims to determine the timing, sequence and conditions of deformations, mineral growth and overprinting of subsequent deformation events. Metamorphic microstructures include textures formed by

2750-583: The strain ellipse. C-planes or cissalement planes form oblique to the shear plane. The angle between the C and S planes is always acute, and defines the shear sense. Generally, the lower the C-S angle the greater the strain. The C' planes are rarely observed except in ultradeformed mylonites, and form nearly perpendicular to the S-plane. Other microstructures which can give sense of shear include Analysis of igneous rock microstructure may complement descriptions on

2805-415: The term "slate" be used in scientific writings only when very little else is known about the rock that would allow a more definite classification. For example, if the characteristics of the rock show definitely that it was formed by metamorphosis of shale, it should be described in scientific writings as a metashale. If its origin is uncertain, but the rock is known to be rich in mica, it should be described as

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2860-408: The thin section and hand-sized specimen scale a metamorphic rock may manifest a planar penetrative fabric called a foliation or a cleavage . Several foliations may be present in a rock, giving rise to a crenulation . Identifying a foliation and its orientation is the first step in analysis of foliated metamorphic rocks. Gaining information on when the foliation formed is essential to reconstructing

2915-456: The town of Lavagna (whose name is inherited as the term for chalkboard in Italian ) and Fontanabuona valley; Portugal especially around Valongo in the north of the country. Germany 's Moselle River region, Hunsrück (with a former mine open as a museum at Fell ), Eifel , Westerwald , Thuringia and north Bavaria ; and Alta , Norway (actually schist , not a true slate). Some of

2970-460: Was used by earlier cultures as whetstone to hone knives, but whetstones are nowadays more typically made of quartz. In 18th- and 19th-century schools, slate was extensively used for blackboards and individual writing slates , for which slate or chalk pencils were used. In modern homes slate is often used as table coasters. In areas where it is available, high-quality slate is used for tombstones and commemorative tablets. In some cases slate

3025-482: Was used by the ancient Maya civilization to fashion stelae . Slate was the traditional material of choice for black Go stones in Japan, alongside clamshell for white stones. It is now considered to be a luxury. Pennsylvania slate is widely used in the manufacture of turkey calls used for hunting turkeys. The tones produced from the slate, when scratched with various species of wood striker, imitates almost exactly

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