Astrophilite with Garnet

Garnets are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different species are pyrope, almandine, spessartine, grossular, uvarovite and andradite. Wikipedia

Color: virtually all colors, blue is very rare

Almandine: Fe3Al2Si3O12

Grossular: Ca3Al2Si3O12

Pyrope: Mg3Al2Si3O12

Spessartine: Mn3Al2Si3O12

Streak: White

Mohs: between 7.5 and 8.5

There are more than twenty garnet categories, called species, but only five are commercially important as gems. Those five are pyrope, almandine (also called almandite), spessartine, grossular (grossularite), and andradite. A sixth, uvarovite, is a green garnet that usually occurs as crystals too small to cut.

Demantoid garnet is the rarest and most valuable of the garnets and is one of the rarest of all colored gemstones. ... The most valuable demantoid comes from Russia, and is distinguished by unique horsetail-pattern inclusions of byssolite. The vivid green color is the most valuable and stones over 1 carat are very rare.

Garnet is the birthstone for January and the gem for the second anniversary.

Garnets are known for their dense, saturated hues. Hence, a great way to distinguish a real gem from a fake one is to look at the color's richness. If your stone is lighter, brighter, or more vivid, then it may be a fake.