Pyrope

Pyrope
General
Category	Nesosilicate
Formula (repeating unit)	Mg3Al2(SiO4)3
IMA symbol	Prp[1]
Strunz classification	9.AD.25
Crystal system	Cubic
Crystal class	Hexoctahedral (m3m) H–M symbol: (4/m 3 2/m)
Space group	Ia3d
Identification
Color	Blood red to black red, red, orange red, pink, some varieties are very dark, almost black, while others can take tones of purple to purple red, Some chromium-rich pyropes are thermochromic, becoming green when heated.[2]
Crystal habit	Euhedra typically display rhombic dodecahedral form, but trapezohedra are not uncommon, and hexoctahedra are seen in some rare samples. Massive and granular forms also occur.
Cleavage	None
Fracture	Conchoidal
Mohs scale hardness	7.0–7.5
Luster	greasy to vitreous[3]
Streak	White
Specific gravity	3.78+0.09 −0.16 [3]
Polish luster	vitreous[3]
Optical properties	Single refractive, often anomalous double refractive[3]
Refractive index	1.74 normal, but ranges from 1.714 to over 1.742[3]
Birefringence	Isotropic, appears black in cross-polarized light
Pleochroism	none
Ultraviolet fluorescence	inert
Absorption spectra	broad band at 564 nm with cutoff at 440 to 445 nm. Fine gem quality pyropes may show chromium lines in the red end of the spectrum
Solubility	Insoluble in water, weakly soluble in HF
Mineral association	Olivine, pyroxene, hornblende, biotite, diamond
References	[4]

The mineral pyrope is a member of the garnet group. Pyrope is the only member of the garnet family to always display red colouration in natural samples, and it is from this characteristic that it gets its name: from the Greek words for fire and eye. Despite being less common than most garnets, it is a widely used gemstone with numerous alternative names, some of which are misnomers. Chrome pyrope, and Bohemian garnet are two alternative names, the usage of the latter being discouraged by the Gemological Institute of America.^[3] Misnomers include Colorado ruby, Arizona ruby, California ruby, Rocky Mountain ruby, Elie Ruby, Bohemian carbuncle, and Cape ruby.