Bloodstone is a green variety of chalcedony (cryptocrystalline quartz), containing red speckles. It is an impure fine-grained quartz whose crystals are too small to see.
The red speckles in the green stone remind some people of drops of blood, leading to a Christian use where bloodstone represents the blood of Jesus. The stone has been used to carve scenes including the crucifixion, from whence came the alternate name, "the martyr's stone". A second alternate name, heliotrope, refers to the way some polished specimens reflect sunlight.
Bloodstone is the traditional birthstone for March, the Zodiac birthstone for Aries, and an alternate for both Aquarius and Pisces. It is associated with endurance.
Bloodstone is only one of several chalcedony (cryptocrystalline quartz) varieties. The primary varieties are as follows: