Agate

Agate (/ˈæɡ.ət/) is a common rock formation, consisting of chalcedony and quartz as its primary components,[1] consisting of a wide variety of colors. Its IMA symbol is Aga.[2] Agates are primarily formed within volcanic and metamorphic rocks. The ornamental use of agate dates back to Ancient Greece in assorted jewelry and in the seal stones of Greek warriors.[3] Use of beads necklaces with pierced and polished agate goes further back to the 3rd millennium BC in the Indus Valley Civilisation.

Agate [Aga]
19.6 kg (43.2 lb) Specimen of "Crazy Lace" agate from Chihuahua, Mexico; the specimen is 38.2 cm (15.0 in) wide
General
CategoryChalcedony variety
Formula
(repeating unit)
SiO2 silicon dioxide
Crystal systemRhombohedral (microcrystalline)
Identification
Colorbanded
Crystal habitCryptocrystalline silica
CleavageNone
FractureConchoidal with very sharp edges.
Mohs scale hardness6.5–7
LusterWaxy
StreakWhite
DiaphaneityTranslucent
Specific gravity2.58–2.64
Refractive index1.530–1.540
Birefringenceup to +0.004 (B-G)
PleochroismAbsent