Hiddenite

What is Hiddenite?

Hiddenite is a pale-to-emerald green variety of spodumene that is sometimes used as a gemstone. Hiddenite is the green gem variety of the mineral Spodumene. Spodumene is a common mineral, but only in several localities does it occur in transparent gem form. One gem form of Spodumene is Kunzite, the other important and much rarer form is Hiddenite. Hiddenite is named after William Earl Hidden, who was instrumental in identifying this new gemstone. The town in North Carolina where this gemstone was found was subsequently given the name "Hiddenite" in honour of the gemstone.

History

Hiddenite was named after W.E. Hidden, who discovered it in 1879 in North Carolina. Hidden travelled to North Carolina to find platinum for Thomas Edison's electric light bulb. Hidden leased Warren Farm to mine emeralds, and found hiddenite. Hiddenite is a green type of spodumene. Spodumene is green, pinkish or lilac and is used as a source of lithium. Hiddenite can appear green-yellow, yellow-green or a striking emerald-green. In fact, hiddenite was also referred to as the "lithia emerald" when mining of it reached its peak in the 1800s. This is because of its vivid green colour. In fact, hiddenite was described in a newspaper in 1892, by Kunz, as being having a "peculiar brilliancy which is wanting in true emerald". Hiddenite is popular with collectors and museums.

Identifying Hiddenite

Hiddenite's pleochroism can help to distinguish it from other gems. A combination of this, its perfect cleavage, hardness, monoclinic crystal system, transparency and colour can distinguish hiddenite from other gems.

Hiddenite: Origin and Gemstone Sources

The mining area of North Carolina, USA, where hiddenite was discovered, has been named Hiddenite, after the gem. The Emerald Hollow Mine in Hiddenite is open to the public. Deposits of hiddenite have also been found in Afghanistan, Myanmar (Burma), Brazil, Madagascar and California.

Properties of Hiddenite

Chemical Formula	LiAlSi2O6
Colour	Green
Hardness	6.5 - 7
Crystal System	Monoclinic
Refractive Index	1.66 - 1.68
SG	3.1 - 3.2
Transparency	Transparent
Double Refraction	.015
Luster	Vitreous
Cleavage	1,2 - prismatic
Mineral Class	Spodumene

Grossular

What is 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.

Hessonite

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

It has a characteristic red colour, 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 Brazil and California.

Deposits

Grossular is found in contact metamorphosed limestones with vesuvianite, diopside, wollastonite and wernerite. A highly sought after variety of gem garnet is the fine green Grossular garnet from Kenya and Tanzania called tsavorite. This garnet was discovered in the 1960s in the Tsavo area of Kenya, from which the gem takes its name.

Viluite is a variety name of grossular, that is not a recognized mineral species. It is usually olive green though sometimes brownish or reddish, brought about by impurities in the crystal. Viluite is found associated with and is similar in appearance to vesuvianite, and there is confusion in terminology as viluite has long been used as a synonym for wiluite, a sorosilicate of the vesuvianite group. This confusion in nomenclature dates back to James Dwight Dana. It comes from the Vilyuy river area in Siberia.

Grossular is known by many other names, and also some misnomers; colophonite coarse granules of garnet, ernite, gooseberry-garnet light green coloured and translucent, olyntholite/olytholite, romanzovite, and tellemarkite. Misnomers include South African jade, garnet jade, Transvaal jade, and African jade.

Properties of Grossular

Chemical Formula	Ca3Al2Si3O12
Colour	White, Colorless, Red, Green, Yellow, Orange, Brown, Pink, Purple, Gray
Hardness	6.5 - 7.5
Crystal System	Isometric
Refractive Index	1.738 - 1.745
SG	3.6
Transparency	Transparent
Double Refraction	None
Luster	Vitreous to adamantine
Cleavage	None
Mineral Class	Grossular (Garnet)