Slate is composed mainly of clay minerals or micas, depending upon the degree of metamorphism to which it has been subjected. The original clay minerals in shale alter to micas with increasing levels of heat and pressure. Slate can also contain abundant quartz and small amounts of feldspar , calcite , pyrite , hematite , and other minerals. Slate roof: Most of the slate mined throughout the world is used to produce roofing slates. Slate performs well in this application because it can be cut into thin sheets, absorbs minimal moisture, and stands up well in contact with freezing water.
A disadvantage is the cost of the slate and its installation in comparison with other roofing materials. As a result, in new construction slate is mainly confined to high-end projects and prestige architecture. Most slates are gray in color and range in a continuum of shades from light to dark gray. Slate also occurs in shades of green, red, black, purple, and brown. The color of slate is often determined by the amount and type of iron and organic material that are present in the rock.
The best way to learn about rocks is to have specimens available for testing and examination. The tectonic environment for producing slate is usually a former sedimentary basin that becomes involved in a convergent plate boundary. Shales and mudstones in that basin are compressed by horizontal forces with minor heating. These forces and heat modify the clay minerals in the shale and mudstone.
Foliation develops at right angles to the compressive forces of the convergent plate boundary to yield a vertical foliation that usually crosses the bedding planes that existed in the shale. School slate: School slate used for writing practice and arithmetic. Students wrote on the slate with a "pencil" made from slate, soapstone , or clay. These slates were widely used until the late s, when wood-case pencils were easily produced and the price of paper became affordable.
The word "slate" has not been used consistently over time and in some industries. Today most geologists are careful not to use the word "slate" when talking about "shale. This confusion of terms partially arises from the fact that shale is progressively converted into slate. Imagine driving your car eastwards in Pennsylvania through areas of increasing metamorphism, starting where the rock is definitely "shale" and stopping to examine rock at each outcrop.
Siltstones are intermediate between sandstones and shales but are not so common as either. They contain less alumina, potash, and water than shales but more silica; in addition to mica, they may contain abundant chlorite and other micaceous clay minerals. What is Siltstone? Siltstone is a sedimentary rock composed mainly of silt-sized particles.
It forms where water, wind, or ice deposit silt, and the silt is then compacted and cemented into a rock. Low-energy, high-oxygen environments e. Grain sizes are smaller than in high-energy environments e. Shale forms in an environment that consists of calm water: for example, water near the shores of large lakes or continental shelves at sea edges. The calmness of the water allows suspended particles like clay to eventually sink and settle in the bottom of the lake or sea.
Sandstone is defined as a rock which is composed of sand-sized grains of various minerals mostly of uniform size and often are smooth and rounded. This weathering breaks the rocks down into clay minerals and other small particles which often become part of the local soil.
Begin typing your search term above and press enter to search. Press ESC to cancel. Skip to content Home Physics Is Slate harder than shale? Ben Davis July 5, Is Slate harder than shale? How do you know if its slate or shale? How can you tell if a rock is shale? Is shale the parent rock of slate? It is a metamorphic rock, being the finest grained foliated of its kind. It is composed mainly of the minerals quartz and muscovite or illite, often along with biotite, chlorite, hematite and pyrite and less frequently, graphite, kaolinite, magnetite, tourmaline, or zircon as well as feldspar.
Quartz, as one of the compositions that build up the slate, is a mineral comprised of silicon and oxygen. Being one of the most-well known minerals on earth, it occurs in basically in all mineral environment and is the important constituents of many rocks. Quartz is also varied from other minerals for it appears in several forms, habits, and colors. Varieties of quartz are usually known as gemstones and are normally used in making jewelry and carvings in hardstone.
Quartz is also a useful mineral because of its physical and chemical properties. Quartz can also be valuable because of its electrical properties and heat resistance that can adhere to the nature of electrical products.
It is very durable because its hardness reaches 7 in Mohs Scale. Quartz is used in glass making, used as an abrasive, also as a foundry sand and used in the petroleum industry because of its high resistance of being crushed that holds the fracture in facilitating natural glass flow.
Known as mica, isinglass, or potash mica, Muscovite, a mineral composition of Slate, is a mineral mixture of aluminum and potassium which is complexly hydrated phyllosilicate. It is present in igneous, metamorphic, and sedimentary rocks which are an important rock-forming mineral.
It is natural to its existence that it readily cleaves into thin transparent sheets. This mineral can be easily identified because it can be easily split into thin, flexible, colorless, transparent sheets since it has a characteristic of perfect cleavage.
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