name: OPAL (Quartz group)
colour: White, gray, blue, green, orange
colour of streak: White
mohs hardness: 5.5-6.5
specific gravity: 1.98-2.20
fracture: Conchoidal, splintery, brittle
crystal system: Amorphous; kidney or grape-shaped aggregates
chemical composition: SiO2.nH2O hydrous silicon dioxide
transparency: Transparent, opaque
refractive index: 1.44-1.46
double refraction: None
absorption spectrum: Fire opal: 7000-6400, 5900-4000
fluorescence: White:white, bluish, brownish, greenish. Black:usually none
Fire:greenish to brown
Technical Data for DIAMOND.
colour: Colorless, yellow, brown, sometimes green, blue, reddish, black
colour of streak: None possible
mohs hardness: 10
specific gravity: 3.47 - 3.55
fracture: Conchoidal to splintery.
crystal system: Isometeric ( cubic ); mainly octahedrons, also
rhombic dodecahedrons, cubes, twins, plates.
chemical composition: C, crystalised carbon.
refractive index: 2.417 - 2.419
double refraction: None, often anomalous.
absorption spectrum: Colorless to yellow: 4780, 4650, 4510, 4350, 4015,
4230, 4155, 3900 Blue-green: ( 5370 ), 5040, ( 4980 )
fluorescence: Variable; Colorless and yellow: mostly blue. Brown
and green: often green.