Canadian Rockhound: Dorfmanite

Dorfmanite is a very rare mineral, first described in 1981 from the Kola Penninsula, Russia. In all of its occurrences (Kola, Mont Saint Hilaire and Tanco), Dorfmanite is a white powder with little evidence of crystal shape. It is the latest mineral to form in the sequence so it is often found as a cavity filling. Dorfmanite is also water soluble so that any samples exposed to the elements, for example on mine dumps, will dissolve quickly. The chemical formula for this mineral is Na₂HPO₄ ^. 2H₂O.

Dorfmanite at Tanco is found in the Lithiophosphate-Tancoite-radial pink Apatite-Cesium Analcime assemblage. This assemblage is relatively rare, but can be identified quickly by the purple-pink colour and radial structure of the Apatite. The phosphates occur as 4 to 5 cm pods in altered Spodumene. Within the phosphate pods the sequence, from the core outward, is:

Lithiophosphate as coarse grained, colourless cleavable masses;
Dorfmanite as a fine grained, white alteration rim which strongly fluoresces bright green colour in short wave U.V. (no response in long wave U.V.);
Radial pink Apatite coating the phosphate nodule.

On some of the phosphate nodules there is a rind of white fine grained alteration products mixed with the pink Apatite. These alteration products include Tancoite.

This series of phosphates is different from a second late suite of Overite-Fairfieldite-Crandallite that occurs at Tanco as well. The phosphate suite at Tanco has no been fully characterized and so may have more surprises.

The Lithiophosphate pods are rare enough that the average collector is not likely to see them. Permission to collect at Tanco must be arranged by contacting the company.

Contact Information

The Tanco Mine can be contacted as follows:

Other Information

Alkali Nuts: Mont Saint-Hilaire
Detailed mineralogical information on Dorfmanite found at Mont Saint-Hilaire, Quebec, Canada.
Mineral Database
Complete and detailed information on the mineralogical properties of Dorfmanite.

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The preceding article was first published in the December 1999 issue of The Mineral Vein, the official newsletter of the Mineral Society of Manitoba. Reprinted in the Canadian Rockhound with permission from the author and editor.