Realgar

Mineral(s): Realgar
Locality: Jiepaiyu Mine (Shimen Mine), Shimen Co., Hunan Province, China

A cluster of deep red realgar crystals to 3.2 cm.

Realgar is the well-known arsenic sulfide mineral that has been used as pigment for many centuries. However, realgar as a pigment is hardly used anymore, since it is an unstable mineral when exposed to air. Over time, the powdery red realgar changes into a yellowish orange mineral called pararealgar (an isomer to realgar).
The instability of realgar is thought to occur due to the arsenic-arsenic (As-As) bonds, being more weak than arsenic-sulfur (As-S) bonds, breaking up from light. As a result, the molecular structure is rearranged to form pararealgar.

I kept this specimen in an enclosed box and so this shot was taken for as short of a time as possible. Though the alteration to pararealgar is almost inevitable, the process takes time. It'll stay red for a while...hopefully.

For the related mineral orpiment, check out my photo here: bmah.deviantart.com/art/Orpime…