Chemical composition -- The garnets comprise a family of complex silicates with widely varying chemical composition but similar structures. While everyone is familiar with dark brownish or purplish red garnets, many are unaware that garnets can occur in almost any color except blue (although there have been some recent reports of some color change garnets that are predominantly blue). Slight variations in chemical composition define the placement of a garnet within the family.
Optics -- R.I. varies with composition, but generally 1.74-1.94. Isometric.
Durability -- Hardness 6.5-7.5.
Crystal structure -- Isometric (cubic).
Specific Gravity -- 3.4-4.2
Varieties -- Many garnets are mixtures of the primary varieties and show variations in properties according to the specific composition.
Dark to very dark purplish, pinkish, or blood-red, usually cut in small sizes (under 2 carats), as larger stones appear black. Czechoslovakia provided huge quantities of "Bohemian" garnet, popular in the jewelry of the late 19th century. Arizona "ant hill rubies" are actually pyrope garnets.
The most common garnet, usually dark brownish to purplish red.
Four- and six-ray star garnet cabochons are supplied primarily
by India and Idaho, with fine six-ray stars being fairly uncommon.
A mixture of pyrope and almandite with a distinctive purplish
red color. North Carolina and Tanzania are major suppliers.
Orange to orange-red. Some of the finest spessartites come from Ramona, California, and Amelia, Virginia, and are rare in large, fine qualities.
A mixture of pyrope and spessartite from the Umba River Valley of Tanzania. Colors vary from orange to peach, pink, or red.
Various shades of orange, green, colorless, yellow, pink. Primarily
from the Umba River Valley of Tanzania.
An orange to brown variety of grossular garnet that has a distinctive swirled, "treacle" appearance under magnification. Major sources include Sri Lanka and Quebec, Canada.
An intense, emerald-like green grossular found only in Kenya and Tanzania. Its color is caused by the presence of vanadium and chromium. Moderately rare in fine stones above a carat or two. The name tsavorite is most popular in the U.S.; tsavolite, in Europe.
Tsavorite is typically found in agglomerations known as "potatoes," such as the example shown here.
A fine green garnet, similar in appearance to tsavorite, but extremely rare in facetable pieces (always small -- under a carat). Highly prized by mineral collectors and seldom seen in finished gems.
Several varieties are known of this rare garnet, the best known
of which is demantoid. Topazolite is an obsolete
name once applied to yellow andradite.
Light to medium green with distinctive fibrous inclusions resembling
horse-tails. Fine demantoids are rare and valuable. The Ural Mountains
were historically the prime source, but there seem to be no active
Light to medium green with distinctive fibrous inclusions resembling horse-tails. Fine demantoids are rare and valuable. The Ural Mountains were historically the prime source, but there seem to be no active sources today.