Hessonite

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Hessonite
Striated crystals of hessonite
General
Category	variety of the grossular species
Chemical formula	Ca3Al2Si3O12
Identification
Crystal system	cubic[1]
Cleavage	none, sometimes indistinct parting[1]
Fracture	conchoidal to uneven[1]
Mohs Scale hardness	7
Polish luster	vitreous[1]
Optical Properties	Single refractive, often anomalous double refractive [1]
Birefringence	none[1]
Pleochroism	none[1]
Specific gravity	3.64 to 3.69

Hessonite or Cinnamon Stone is a variety of grossular, a calcium aluminium mineral of the garnet group with the general formula Ca₃Al₂Si₃O₁₂. The name is from the Greek hēssōn, inferior, in allusion to its lower hardness and density than most other garnet species varieties.

It has a characteristic red color, inclining to orange, much like that of gem zircon. Indeed it was shown many years ago, by Sir A. H. Church, that many gems, especially engraved stones, commonly regarded as zircon, were really hessonite. The difference is readily detected by the specific gravity, that of hessonite being 3.64 to 3.69, whilst that of zircon is about 4.6. Hessonite has a similar hardness to that of quartz, about 7 on the mohs scale, whilst the hardness of most garnet species can reach 7.5.

Hessonite comes chiefly from Sri Lanka, where it is found generally in placer deposits, though its occurrence in its native matrix is not unknown. It is also found in Brazil and California.

[edit] References

1. ^ ^{a b c d e f g} Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN:0-87311-019-6

• Mineral galleries
• This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.