By Bill Shelton
Colors in Garnets
Perhaps, we can find 10 major colors in garnets that belong to the six main species recognized by many sources. What are the colors and which species are noted to occur in those colors? Well, it appears that as one might guess that red is most common and will be seen in five out of six species.
The six species we refer to are almandine, andradite, grossular, pyrope, spessartine and uvarovite.
Red is never seen in uvarovite but will occur in all the others. Pink is noted for three species – they are andradite, grossular and pyrope. Orange, a nice color for garnet, is present in grossular and spessartine. Yellow will likely occur in andradite and grossular. Green, a personal favorite, is noted in andradite, grossular and uvarovite where it is also the only color to be seen. Purple is unique to pyrope; however there are hints in certain almandines. Brown, not a collector favorite, can occur in andradite, grossular and spessartine. Black is mainly noted for andradite but a few grossulars may be this color. Colorless garnet would be a rare thing in a general sense; pure grossular does exhibit this color now and then. White rarely is found and when it is, expect the species pyrope and grossular to be present. So, the winner is grossular with a total of 15 different shades. I suppose uvarovite is the big loser with only one shade. Almandine has three, andradite has eight, spessartine has six and pyrope has four.
The exact cause of the various colors is suggested to be due to chemicals present in the garnet. Iron may impart red and yellow-green; yellow, orange and black (often with titanium); also purple when chromium is also present as well. Chromium is also thought to cause green and notably in uvarovite where this is the only color we see. Vanadium will be credited with yellow-green; manganese is responsible for pink and orange. You may note that more than one cause is given for some colors. The odd alexandrite effect may be due to chromium, vanadium and manganese together.
Various sources list the following colors for grossular. They are pink, red-brown, orange, yellow, pale green, emerald green, greenish-blue, colorless (or nearly so), olive green, cherry red, dark green, honey brown brown orange-brown and black. I find the colorless and white garnets to be a peculiar thing – the explanation is said to be due to the lack of chromophores and is limited to pyrope and grossular when they are pure. There is no iron or manganese; also no chromium or vanadium which all can be suspected causes of color in garnets.