4. Garnet

1. Isometric (cubic) crystal system

1. Crystal system with greatest symmetry

1. All three axes same length
2. All three axes are mutually perpendicular
3. Four-fold symmetry

1. Singly refractive (SR)

1. Isometric (only SR crystal system)
2. Light entering the stone from every direction travels through the crystal at the same velocity

1. Chemical composition

1. Garnet group has six species divided into two series based on chemical composition.

1. All garnets have basically the same structure, but different chemical compositions.
2. Chemical group for garnet is silicate.
3. All garnets can intermix within and between the two series.
4. A garnet species designation is often arbitrary, based on the refractive index, specific gravity, and/ or color.
5. Some garnets have no identifiable species and are called just a garnet.

1. Species, varieties, and trade names.

1. Pyrope – Almandite – Spessartite series.

1. Pyrope species

1. Name from Greek "pyropos", meaning "fiery-eyed" or "fire-like".
2. Generally the purest red color for a garnet and can be confused with ruby.

1. Almandite species

1. Never occurs pure in nature, but all garnets near the pure almandite composition called almandite; therefore it is the most common garnet species.
2. One variety, a phenomenal variety, is the star almandite, with 4 or 6 rays.

1. Rhodolite variety

1. Variety of garnet, not species
2. Mixture in composition between pyrope and almandite
3. Must have color of red-purple, reddish-purple, or purple to be called rhodolite.
4. Popular gemstone

1. Spessartite species

1. Typical colors are yellow-orange, orange, orangish-red, orangish-brown, or reddish-brown.
2. No varieties
3. Malaya garnet (malaia) is a trade name for garnets of a particular color from East Africa.

2. Grossularite – Andradite – Uvarovite series

1. Grossularite species

1. Has more colors than the other garnets and can be transparent to nearly opaque.
2. Two popular and expensive varieties.

1. Hessonite: transparent yellow-orange, reddish-orange to orange-brown
2. Tsavorite: transparent intense green to yellowish-green

b. Andradite species

1. Typical colors are yellow-green, brown, black, and green
2. Demantoid variety

1. Must be light to dark green to yellowish-green
2. One of the rarest gems, especially in large sizes and darker tones

c. Uvarovite species – dark green garnet with crystals always too small for gemstone material.

1. January birthstone

E. Name garnet

1. Latin "grantum" meaning "seed-like" or "having many seeds"
2. Garnet crystals reminded early scientists of the shape and color of pomegranate seeds.
3. Pre-Christian era and in the Bible, garnet is called ruby and Carbuncle.

1. Gemlore

1. Gem of faith, constancy and truth
2. Medicinal belief

1. Fever, jaundice
2. Travelers amulet to preserve health

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