Amethyst cluster, February birthstone

A cluster of naturally coloured purple amethyst crystals from Brazil. This is actually the end of a stalactite or stalagmite. Do you know how to tell which is which in situ? A stalactite has to hold on tight, a stalagmite might reach the roof. Amethyst is a February birthstone.

15/16 inch (2.4 cm) wide, 13/16 inch (2.0 cm) deep and 3/8 inch (0.95 cm) tall.