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SLATE is a very fine grained metamorphic rock derived from sedimentary rock shale. Characterized by an excellent parallel cleavage entirely independent of original bedding, by which cleavage the rock may be split easily into relatively thin slabs. The principal characteristic of slate is how it splits into thin, broad sheets. The minerals that form the slates, are mainly quartz and muscovite. The slate tends to be of bluish black color or grayish black, but exist red varieties, green and other tones. Slate used in roofs, flooring and even for decorative elements GROUP Metamorphic
COMMON ROCK-FORMING MINERAL GROUP Silicates
COMPOSITION Muscovite, chlorite, kaolinite, micas, quartz and other accessory minerals.
HARDNESS Soft to as Hard and dense as granite
MOHS' SCALE 2.5 - 5.5 POROSITY 0.4 - 5 % ABSORPTION 0.1 - 1.7 % WEATHERING CHARACTERISTICS Due to the wide ranges of slate, this stone has wide ranges of weathering. Cleft planes provides permeability for water penetration resulting in spalling and flaking. Slates that have a high kaolinite content (a clay) display accelerated rate of deterioration in wet environments. TENDENCIES Absorbs oils and liquids and get scratches easily. COLORS Colors very widely. FINISHES Natural Cleft...Honed...Some types my be Flamed. NOTATIONS Sealing to minimize staining...Colored slates benefit from color enhancing treatments designed to magnify and protect the natural colors. When dealing with colored slates there are two distinct types, Fading and Unfading. After a period of exposure to the environment (sun/water) fading slates will alter generally to a lighter color. The unfading varieties will retain their true colors. Multi-colored slates used for flooring will undergo color changes in abrasive foot-traffic areas. The colors in these varieties of slates are in thin bedded layers...Some slates will dust for awhile after installation on floors as loose scale is removed by foot traffic. This will stop as the surface settles in, usually in a few weeks. The majority of the multi-colored slates are what are termed "clay slates" and generally have a high content of clay minerals and are geologically classed as a low-ranked slates, those in which the metamorphic process was halted at a very early stage. These slates weather poorly in exterior wet/humid climates.
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