garnet

Garnet is a group of minerals with six main members:

Pyrope, Almandine, Spessartine, Grossular, Andradite and Uvarovite. Please see separate entries.

All of the members of the group, except Uvarovite, may be cut as faceted stones or cabochons. Uvarovite is an emerald-green garnet that occurs in very small crystals, formed on a host rock called a druse. Although the individual crystals are too small to fashion, the druse itself can be cut and mounted into suitable jewellery settings.

Most garnets are a mixture of species/varieties giving rise to a variation in their optical and physical properties. When that mixture is well defined i.e. there is an ample amount of each defining chemical element present. Then the garnet is defined as a separate member of the garnet group.

Garnets of this type include:

Malaya:                       Malaya garnets are a mixture of spessartine and pyrope, producing
                                     orange to reddish-orange stones.
Colour Change:        Colour Change Garnets are also a mixture of spessartine and
                                     pyrope, but produce stones that appear green in sunlight and red in
                                     incandescent light (filament light bulb).
Mali:                            Mali garnet is mainly grossular with some andradite producing green to yellow
                                     stones.
Rhodolite:                  Rhodolite garnet is a mixture of almandine and pyrope producing rose or
                                     raspberry red to violet coloured stones.

Properties of the Gemstone and Additional Information

Gemstone type: The Garnet Group
Crystal System: Cubic (isometric) commonly occurring as rhombic dodecahedron and icositetrahedron crystals
Chemical Composition: See individual entries
Colour: Garnets occur in all colours except blue. Colourless stones are called leuco garnets, a variety of grossular garnet
Lustre: See individual variety entries
Pleochroism: Absent
Dispersion: Medium
Hardness: See individual entries
Toughness: Fair to good
Cleavage: None
Density in gm/cc: See individual entries
Double refraction: None
Refractive index: See individual entries

Common Treatments

Garnets are not normally treated.

Composite stones called garnet topped doublets are made, comprising a crown (top section of the faceted stone) of natural garnet and the pavilion (lower section of the stone) of glass. Almandine or pyrope garnet is normally used for the crown section.
A close-up inspection will reveal the join and a change in lustre between the garnet and glass. Bubbles are normally visible in the glass and/or glue between the two layers. Inclusions seen in the crown that are characteristic of garnet will not be seen in the pavilion.