Minerals ~ Garnet var. Hessonite (Grossular)
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Striated crystals of hessonite, a variety of the grossular species
Photo Credit: Aram Dulyan
Garnet var. Hessonite (Grossular)

Grossular is a calcium-aluminium species of the garnet group of minerals. It has the chemical formula of Ca3Al2(SiO4)3 but the calcium may, in part, be replaced by ferrous iron and the aluminium by ferric iron. The name grossular is derived from the botanical name for the gooseberry, grossularia, in reference to the green garnet of this composition that is found in Siberia. Other shades include cinnamon brown (cinnamon stone variety), red, and yellow. Grossular is a gemstone.

Grossular should not be called grossularite, grossularite was once a type of rock.


Hessonite or Cinnamon Stone, is a more common variety of grossular with the general formula: Ca3Al2Si3O12. The name comes from the Greek hēssōn, meaning inferior; an allusion to its lower hardness and lower density than most other garnet species varieties.

It has a characteristic red color, inclining to orange or yellow, much like that of zircon. It was shown many years ago, by Sir Arthur Herbert Church, that many gemstones, especially engraved gems (commonly regarded as zircon), were actually Hessonite. The difference is readily detected by the specific gravity, that of Hessonite being 3.64 to 3.69, while that of zircon is about 4.6. Hessonite has a similar hardness to that of quartz (being about 7 on the mohs scale), while the hardness of most garnet species is nearer 7.5.

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

SOURCE


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