Paper No. 3
Presentation Time: 8:50 AM

DYPINGITE MG5(CO3)4(OH)2▪5H2O FROM RAPID CREEK, YUKON, CANADA. CHEMICAL COMPOSITION, OPTICAL PROPERTIES AND COMPARISON WITH SIMILAR HYDRATED MAGNESIUM CARBONATES


PETERSON, Ronald C., Geological Sciences and Geological Engineering, Queen's University, Miller Hall, Kingston, ON K7L3N6, Canada, TAIT, Kimberly, Department of Natural History, Royal Ontario Museum, Toronto, ON M5S 2C6, Canada and NICKLIN, Ian, Natural History, Royal Ontario Museum, 100 Queen's Park, Toronto, ON M5S 2C6, Canada, peterson@geol.queensu.ca

Dypingite Mg5(CO3)4(OH)2▪5H2O, closely associated with hydromagnesite Mg5(CO3)4(OH)2▪4H2O, was collected from an open fracture system above permafrost near Rapid Creek, Yukon, Canada in August 2012. The Rapid Creek area lies within the Richardson Mountains of the northeastern Yukon Territory, Canada, near the border with the Northwest Territories. There have been seven new minerals discovered there such as arrojadite-(K,Na), gormanite and kulanite; some of these minerals have never been found anywhere else in the world. Dypingite occurs on the fracture surfaces with a botryoidal habit consisting of fine radiating crystals forming a translucent crust of spheroidal aggregates. Some the spheroids can be up to 1 mm in diameter. The dypingite is often covered with loose and chalky hydromagnesite that is brittle and falls away from the fracture surface. The relationship suggests that the hydromagnesite forms as a dehydration product of dypingite at this locality.

Several mineral species belong to the hydrous magnesium carbonate mineral group. Anhydrous magnesite MgCO3 is followed by barringtonite MgCO3▪2H2O , nesquehonite MgCO3▪3H2O and lansfordite MgCO3▪5H2O as hydration increases. Pokrovskite MgCO3(OH)2 and Mcguinnessite (Mg,Cu)CO3(OH)2 have hydroxyl as an additional anion. Dypingite Mg5(CO3)4(OH)2▪5H2O, hydromagnesite Mg5(CO3)4(OH)2▪4H2O and artinite Mg5(CO3)4(OH)2▪3H2O have both hydroxyl and water as essential components. The relationship between mineral composition and physical properties of these minerals is discussed. As expected, the mean refractive index is found to be lower in mineral species containing more water and the unit cell volume normalised to magnesium content increases with increased water. Increase of OH within in these mineral structures does not cause a similar decrease in mean refractive index or an increase in cell volume normalized to magnesium atoms per formula unit. Gladstone-Dale calculations show agreements of excellent or superior for all minerals except barringtonite where the agreement is good according to the classification scheme of Mandarino (2007).Attempts to synthesis dypingite are in progress. Comparison of the atomic structures of these chemically similar phases is used to suggest possible atomic structures for dypingite.