Carletonite

Carletonite is an extremely rare silicate mineral. So far, it has only been found in one location worldwide: the classic mineral locality of Mt Saint-Hilaire, Quebec, Canada. The mineral was identified in 1971 by G.Y.Chao of the Department of Geology, Carleton University, Ottawa, Canada, and was named for the university.

Cartelonite is found in pale to deep blue, pink to colorless and white. Color zoning with a gradual or very sharp and irregular transition is quite common for this type of mineral.Cartelonite is formed from Hydrated Potassium Sodium Calcium Carbonate Silicate Fluoride Hydroxide [KNa4Ca4(CO3)4Si8O18 (F, OH) - H2O]. Its crytals can be dull to vitreous and transparent to translucent. The mineral has a low hardness of 4.5 - 5 on the Moh’s Scale with a Specific Gravity of approximately 2.45.Carletonite belongs to the Apophyllite group of minerals. In addition to Carletonite, members of the group include: Fluorapophyllite, Hydroxyapophyllite and Natroapophyllite. Like other Apophyllites, Carletonite has an interesting crystal structure. The crystals are layered with alternating silicate sheets and the potassium, sodium and calcium layers.

Another interesting characteristic of Carletonite is that the darker blue crystals often show pleochroism which is a condition in which the color of the crystal will change depending on the angle it is viewed. Carletonite demonstrates a blue to pinkish-brown pleochroism.

At Mt Saint-Hilaire, Carletonite has been found as inclusions in Nepheline Syenite. The mineral mainly occurs in association with Pectolite, Albite, Arfvedsonite, Calcite, Fluorite, and Apophyllite. Crystals of Carletonite have been cut as gems, but they are mostly collected as rare mineral specimens.