Garnet is a very beautiful and colourful gemstone but did you know there are so many garnet Varities? It can be confusing to understand what is what. Some Garnets you might have heard of include Tsavorite, Demantoid, Rhodolite, Spessartite, Hessonite and Topazolite. These are all Garnets, but they each have their own unique properties and colour.
Let’s first look at why Garnet occurs in so many different colours and varieties. Garnet is the family name given to two groups of three isomorphic minerals. The six different minerals are all classified as Garnet (actually there are 15 minerals, but only six produce gem quality material).
Garnets are all isomorphic. This means that between each mineral, they all have the same crystal habit, but slightly different chemical makeup. Let’s look closer.
The first group under the Garnet family is the Pyralspites (minerals Pyrope, Almandine, Spessartite). The second group is the Ugrandites (minerals Uvarovite, Grossular, Andradite).
Pyralspites: Only slightly different chemical makeup between minerals
- Pyrope (magnesium aluminum silicate)
- Almandine (iron aluminum silicate)
- Spessartite (manganese aluminum silicate)
Ugrandites: Only slightly different chemical makeup between minerals
- Uvarovite (calcium chromium silicate)
- Grossular (calcium aluminum silicate)
- Andradite (calcium iron silicate)
The easiest way to understand what Garnets are from which family is by using diagrams. Below shows how each of the minerals give a certain colour and appearance.
From the diagrams above, it is clear to see what colour pure Almandine or Pyrope Garnet is. However, as the two minerals mix together, they can produce a purple Garnet known as Rhodolite Garnet, which is actually Pyrope-Almandine Garnet.
There are an almost infinite number of different Garnets when each of these minerals mix together in certain ratios. This is why there are so many different and beautiful types of Garnets.