Arizona-Sonora Desert Museum Digital Library

Northupite

Northupite, (Na₃Mg(CO₃)₂Cl), Isometric. It occurs as octahedrons of up to 2 centimeters in size and as globular masses. It is brittle with a conchoidal fracture, a hardness H of 3½ – 4, and a density of 2.4g/cc. It slowly decomposes in water leaving a magnesium carbonate residue.

It has a vitreous luster and is transparent to translucent. It is colorless, but can be pale green if ferroan. Owing to inclusions, it may be pale yellow, gray, or brown.

The mineral is uncommon and formed at 20°C to 50°C as a lacustrine deposit, or in the subsurface in mud and clay. It may be a replacement of earlier saline minerals. It is a mineral of playa lakes and their sediments and subsurface. It is associated with other minerals of similar composition that include shortite, trona, andsearlesite.

It is known in the U.S.A. from Searles and Borax Lakes in California and in Sweetwater County, Wyoming. It is known from lakes in Uganda and Chad. It is a product of salt mines of Bosnia and is reported on Ross Island of the Ross Sea in Antarctica. It is not yet reported in Arizona.

It is named to honor Charles H. Northup (1861 - ?) grocer of San Jose California who found the first examples.

Ref. 1, SRT.