Slate
Mineral NameSlate
Chemical FormulaComplex, primarily silicates (quartz, muscovite, chlorite)
Mohs Hardness2.5
Streak ColorGray to black, matching rock color
CleavagePerfect slaty cleavage, splitting into thin, flat sheets
FractureUneven to splintery across the grain
Specific Gravity2.75
Colorsgray, black, green, purple, red
TransparencyOpaque
Type LocalityWales (UK), Vermont (USA), Pennsylvania (USA), Brazil
Mineral GroupMetamorphic rock
Usesroofing, flooring, blackboards, decorative stone, landscaping
Associated Mineralsquartz, muscovite, chlorite, illite, hematite, pyrite
Raritycommon
Description
The image shows a block of gray-green slate with a rough, textured surface, exhibiting its characteristic fine-grained appearance and potential for slaty cleavage.
Geological Context
Slate is a fine-grained, foliated metamorphic rock formed by the low-grade regional metamorphism of shale or mudstone. The intense pressure and relatively low temperatures cause the clay minerals to recrystallize into micas and chlorite, aligning perpendicular to the stress, which creates its distinctive slaty cleavage.
