Jasper

Jasper
Jasper outcrop, Bucegi Mountains, Romania
General
Category	Aggregate rock (impure chalcedony variety)
Formula	SiO2 (with varying impurities)
Crystal system	Hexagonal
Identification
Colour	Most commonly red, but may be yellow, brown, green or (rarely) blue
Cleavage	Indiscernible
Mohs scale hardness	6.5–7
Luster	Vitreous
Diaphaneity	Opaque
Specific gravity	2.5–2.9
Refractive index	1.54–2.65
Birefringence	0.009

Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases,^[1][2] is an opaque,^[3] impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. The common red color is due to iron(III) inclusions. Jasper breaks with a smooth surface and is used for ornamentation or as a gemstone. It can be highly polished and is used for items such as vases, seals, and snuff boxes. The density of jasper is typically 2.5 to 2.9 g/cm³.^[4] Jaspillite is a banded-iron-formation rock that often has distinctive bands of jasper.