Almandite
Garnet
Garnet, Its name comes from
Latin granatus meaning seed, because it often resembles small
round seeds when found in its matrix rock.
Rather than a single gemstone, garnet is a family of related minerals,
some of which occur as gemstones.
Each has a common crystal structure, and a similar chemical composition.
General
Colour
Garnet occurs naturally in a large range of colours including: red,
orange, brown, green, yellow, and brown.
Chemical Composition and
Name
Almandite is an iron aluminium silicate, 3FeO . Al2O3
. 3Si2
Pyrope is a magnesium aluminium silicate
Spessartite is a manganese aluminium silicate
Andradite is a calcium iron silicate.
Grossular is a calcium aluminium silicate
Uvarovite is a calcium chromium silicate.
Two Families of Garnet
There are two main theoretical groups or "families" of garnet:- pyrope,
almandite, spessartite, which are all (metal) aluminium silicates, and
uvarovite, grossularite, andradite, which are all calcium (metal)
silicates.
Trade Terminology
In the trade, gem dealers hardly ever refer to their stock as "pyrope"
or "almandite". Instead, they will often refer to "brown" or Indian
garnets. Rhodolite garnets are usually about midway along the
pyrope-almandite axis.
