Garnet is a mineral group that can range in color from red, pink, orange, yellow, greenish brown to black. While some feel these varieties should be looked upon as different minerals, the fact remains that without exception, all garnets possess the same structure, and they are ALL in the cubic crystal system. In addition, no matter the color, all are formed during the formation of crystalline slates or other metamorphic rocks.
All Garnets are in the mineral class of island silicates. Even in the variation of their formations, three laws are always followed. Each is made of two-valency metal ions, three-valency metal ions and the island silicate modules, and always in the ratio of 3:2:3. The addition of a 4th element like iron or aluminum provides the color (green through pink from aluminium, brown through black from iron).