Crystal Mimicry – The ability to have a crystal body.
Blue Diamond (DC) had a body with diamond like hard skin but was later turned into a living diamond (Official Handbook of the Marvel Universe #1, 2004).
Emma Frost (Marvel) is a powerful telepath but in her diamond form can take on a more physical approach in a fight but appears to have meet her match in the picture below.
Crystar (Marvel) comes from world were crystal forms and crystals are common but not paper and wood (Crystal Warrior V1 #3).
In Prophet-Earth War #4 (Image), normal monsters are transformed into Crystal monsters!
Batman fights a Crystal Creature in Detective Comics V1 #272.
Martinex (Marvel) has been genetically engineered to be a crystal humanoid that can withstand the rigors of Pluto (Official Handbook of the Marvel Universe V1 #7).
The Living Diamond (Marvel) appears in Uncanny X-Men V1 #42.
The Shardmind is a being made of crystal in the D&D universe (D&D 4th Edition – Monster Manual 3).
Darkling Sentinel – Creature Collection II. Dark Menagerie
Diamond Demon – Archie’s Madhouse #37 (1964)
Herculoids – Hanna Barbara Super TV Heroes #5
Jewel Gang – Archie’s Madhouse #46 (1966)
Nerra – D&D 4th Edition – Monster Manual 3
Crystal beings are well represented in Trade Card Games.