Mineral Information and Data:

Andradite
Ca3Fe3+2(SiO4)3 [CNMNC approved formula]

Named for José Bonifácio de Andrada e Silva (1763-1838), Brazilian mineralogist.

IMA status : Valid species (Pre-IMA 1868) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
51.04.03b.01  
  (51) Nesosilicate Insular SiO4 Groups Only
  (51.04) with cations in [6] and >[6] coordination
  (51.04.03b) Garnet group (Ugrandite series)
  
Nickel-Strunz
(10th edition) :
09.AD.25
  (09) Silicates
  (09.A) Nesosilicates (Isolated tetrahedron) structures
  (09.AD) Nesosilicates without additional anions; cations in [6] and/or greater coordination
  
Crystal system: Cubic System
Point group (H-M): m3m (or 4/m 3 2/m) — hexoctahedral
Unit cell: a = 12.06 Å
Crystal Habit: Crystals usually dodecahedrons or trapezohedrons; massive; granular
  
Color: Hades of yellowish green, green, brown, red-brown, black
Diaphaneity: Transparent to translucent
Luster: Vitreous, adamantine to resinous
Hardness (Mohs): 6.5 to 7
Measured Density: 3.8 to 3.9 g/cm3
Cleavage: None
Tenacity: Brittle
Fracture: Uneven to conchoidal
Streak: White
  
Geologic Setting: In skarns from contact metamorphosed impure limestones or calcic igneous rocks;
in chlorite schists and serpentinites; in alkalic igneous rocks, then typically titaniferous
Mineral Association: Vesuvianite, chlorite, epidote, spinel, calcite, dolomite, magnetite
  
Synonyms/varieties: Melanite (black Ti-rich variety), topazolite (yellow variety), demantoid (green gem variety)
Other Properties: Gemstone Readily Available.
Comments: Series with grossular and with schorlomite.

 

Andradite
Variety melanite
Origin: New Idria district, San Benito Co, California, U.S.A.
Owner: Natural History Museum of Los Angeles County
Sample size: crystals up to 1 cm
Photo: Anthony Kampf, Natural History Museum of Los Angeles County

 

Andradite
Origin: Junnila mine, New Idria district, San Benito Co, California, U.S.A.
Owner: Natural History Museum of Los Angeles County
Sample size: largest crystals are about 0.8 mm
Photo: Anthony Kampf, Natural History Museum of Los Angeles County

 

Andradite
Demantoid on serpentinite
Origin: Val Malenco, Sondria, Lombardy, Italy
Sample size: 3.5 x 6.8 x 2.5 cm
Photo: Dan Weinrich

 

Andradite
(zoom-in of above)

 

Andradite
Origin: N'Chwaning Mine, Kalahari Mn Fields, North Cape Prov., South Africa
Sample size: 3.5 x 3 x 2.5cm
Photo: Tom Loomis

 

Andradite
(zoom-in of above)

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