Congolite - Sold
- 2.9 by 1.6 by 1.6 cm – Thumbnail specimen (fits into a 3 cm cube)
Congolite is a rhombohedral analog of ericaite; it is an iron borate chloride. At high temperature, when it forms, the mineral has cubic symmetry. But on cooling the atoms in the crystal shift, and the symmetry reduces to rhombohedral (hexagonal). Originally thought to be ericaite, recent study has shown that these specimens are actually rhombohedral (Dowty and Clark, 1973). This is a rare matrix example of congolite, with a 3 mm cube embedded in halite. There may also be anhydrite present. This specimen was part of the personal collection of Ralph Merrill, proprietor of the prolific mail order business Minerals Unlimited, obtained in 1963. Merrill's collection card and label also ship with the specimen.