Agate

Agate
Moss agate pebble, 2.5 cm (1 inch) long
General
Category	Quartz variety
Chemical formula	Silica, SiO2
Identification
Color	White to grey, light blue, orange to red, black.
Crystal habit	Cryptocrystalline silica
Crystal system	Rhombohedral Microcrystalline
Cleavage	None
Fracture	Conchoidal with very sharp edges.
Mohs scale hardness	7
Luster	Waxy
Streak	White
Specific gravity	2.58-2.64
Refractive index	1.530-1.540
Birefringence	up to +0.004 (B-G)
Pleochroism	Absent

Agate