Back-scattered electron image of thin veins of near-endmember rossmanite (dark grey) cross-cutting the host elbaite (medium grey). Image courtesy of Ai Cheng Zhang.
Rossmanite occurs in an albite (cleavelandite variety)- spodumene zone as thin veinlets (10 to 20 micrometers wide) within the main mass of 1 to 3 cm light pink elbaite crystals. Its formation is believed to be the result of the interaction of late stage, Na- and Ca-deficient hydrothermal fluids passing through and filling pre-existing cracks in the elbaite.
These veinlets of rossmanite are noteworthy for their low Na and Ca contents. One analysis point revealed an X-site vacancy of 1.00, indicating that it was nearly pure rossmanite. This is the composition closest to end-member rossmanite reported to date.
A typical composition is
X(0.95Na0.04Ca0.01) Y(Li0.94Al1.93Fe0.09Zn0.03) ZAl6.00 (BO3.00)3.00 Si6.00O18.00 [(OH)3.95F0.05]
Zhang AC, Wang Ru, Hu H, Chen XM (2004) Occurrences of foitite and rossmanite from the Koktokay No. 3 pegmatite dyke, Altai, Northwestern China: A record of hydrothermal fluids. Canadian Mineralogist, 42, 873-883.
last upgraded: 14-Dec-2019