Ettringite (Matrix!)
Toenail, 3.0 x 3.0 x 1.6 cm
N'Chwaning Mine, Northern Cape Province, Republic of South Africa

Well-crystallized ettringites are uncommon in the first place, but this specimen is notable for the fact that it is a MATRIX specimen (so many are standalone crystals). It features a sharp, bright yellow, complete and terminated crystal measuring one centimeter in each direction, perched atop the matrix.