Purple crystals appear in two forms, normal and large. The normal purple crystal is a small, three-pronged crystal and the large form is a tall, thin crystal with different shades of purple.
How to Obtain
The Purple Crystal can be found in any world type and is found underground in small caves. It lets off a low purple glow, helping players to find them. To obtain it you just have to mine it. But be careful: they will deal the same damage as stalagmites and can kill you if you're on low health.
The normal purple crystal is used in crafting purple crystal blocks, and in many engineering items. The large purple crystal is decorative only.