Slate is a very fine-grained (less than 0.5 millimeter) foliated rock composed of tiny flakes of mica that are too small to be visible. It belongs to the group of metamorphic rocks.
Therefore, it generally appears opaque and closely resembles shale and siltstone. The board it is most frequently generated by low-grade metamorphism (zeolite to greenschist metamorphic facies) originating from shale or siltstone.
Less frequently, it occurs when volcanic ash (tuff) metamorphoses.
Thin sheet slate
It shows a board polarizing microscope view (thin slide). It is characterized by having a well-developed crenulation cleavage, where the micas, mainly chlorite biotite, elongate in the direction of the cleavage.
Cleavage develops perpendicular to regional stress. The board it contains muscovite-sericite, chlorite, biotite and a low content of graphite (graphite material).
Properties and characteristics
The board It is an extremely dense form of fine-grained metamorphic rock under regional low-grade metamorphism arising from pelitic sedimentary rocks such as fine-grained shales and tuffs.
The pre-crystallization level of primary minerals witness very weak changes under the increase of only directed pressure and low temperature.
Texture
A notable feature of the board it is its well-developed cleavage, or its tendency to break into planes. It is characterized by well-developed cleavage, which is generally difficult to differentiate from laminated pelitic sedimentary rocks.
This metamorphic texture is caused by the parallel orientation of small microscopic sheets of illite and chlorite.
Slate mineral components
These metamorphic rocks largely retain the primary mineral composition and structure of the original rocks, except for a smaller or larger part of typical, partially or fully recrystallized clay minerals such as illite, sericite, and chlorite.
The most common minerals are: quartz (between 20% and 30%, confers hardness to the rock), illite and chlorite (those that confer cleavage). In addition, they have hematite, pyrite, graphite and carbonaceous substances (those that provide heat and thermal conductivity).
To a lesser extent they contain feldspar, biotite, rutile, siderite, tourmaline, zircon, andalusite and kaolinite. The minerals that give it industrial use are: pyrite, calcite and dolomite. The first tends to oxidize and generate sulfuric acid that dissolves carbonates, reducing its industrial quality.
Composition
The color of the depends on its mineral components. Black (carbonaceous) slate contains organic material; red gets its color from iron oxide; and green slate generally contains chlorite. It is composed mainly of clay minerals or micas, depending on the degree of metamorphism to which it has been subjected.
The original clay minerals in the schist alter to micas with increasing levels of heat and pressure. Shale may also contain abundant quartz and small amounts of feldspar, calcite, pyrite, hematite, and other minerals.
Source
The tectonic setting for the formation of board it is usually an old sedimentary basin that becomes involved in a convergent plate boundary. The shales and siltstones 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 produce a vertical foliation that generally crosses the bed planes that existed in the protolith..
Applications
The cleavage of the slates makes it possible to separate into sheets between 2.5 and 5 mm thick for house roofing and wall cladding. Also wainscoting, electrical panels, steps, pedestals, flagstones, thresholds, headstones and pool tables.
It is also used in the manufacture of lightweight cellular aggregates for concrete, asphalt mixes, for the construction of acoustic tiles, lime brick and slate. It is also used as a filler in the manufacture of paints and other products.
One drawback is the cost of slates and their installation compared to other roofing materials. As a result, in new construction, slate is mostly limited to high-end projects and prestigious architecture.
Slate is also used for interior flooring, exterior paving, dimension stone, and decorative aggregate. Historically, slate board It has been used for chalkboards, student writing boards, pool tables, graveyard markers, sharpening stones, and table tops.
Because it is a good electrical insulator, it was also used for early electrical panels and switch boxes.