Monday, May 25, 2009

June Mineral of the Month

'Garnet Group'

Garnet is named from the word 'grantum', meaning pomegranate, for its resemblance to the fruit's seeds.

The Garnet mineral group is compromised of isomorphous minerals identical in crystal structure and in many cases difficult to determine one from another. The members of this group intermingle with one another, within limits.

The most common Garnet members are Pyrope-Mg3Al2Si3O12 Alamandine-Fe2+3Al2Si3O12 Spessartine-Mn3Al2Si3O12 Andradite-Ca3Fe3+2Si3O12 Grossular-Ca3Al2Si3O12 and

There are seven lesser known members of the Garnet family known as Knorringite, Majorite, Calderite, Goldmanite, Schorlomite, Kimzeyite & Morimotoite. There are also two hydro garnet members know as Hibschite and Katoite. These nine members are extremely rare and very little is actually known about them.

Garnet crystals are dodecahedral or trapezohedral in form. They usually form as rounded grains and come in a variety of colors depending on the individual variety. They can also form in massive, granular or compact habits

Garnets are a member of the silicates group. They have a hardness of 6-1/2 to 7-1/2 on the Mohs scale. Garnets have no cleavage and and un-even to conchoidal fracture. It's specific gravity is 4.1 to 4.3. Garnet has a white streak and is transparent to opaque and has a vitreous luster.

Garnets form in a variety of ultrabasic igneous rocks, associated serpentines & metamorphosed rocks such as schist.

Garnet fuses fairly easily and is virtually insoluble in acids. Garnet is one of the only gemstones on the planet that is not heat treated or irradiated or undergoes any other type of man made process in order to enhance the quality of the finished gemstone.