Tourmaline var. Rossmanite from Tanco Mine, Manitoba, Canada (D)

Stunning large specimen of rare tourmaline var. rossmanite from Tanco Mine, Bernic Lake, Manitoba, Canada.

Rossmanite is a rare lithium-rich member of the tourmaline group with the chemical formula (LiAl₃Al₆(Si₆O₁₈)(BO₃)₃(OH)₃OH). Unlike most tourmalines, it is alkali-deficient, with the sodium site vacant. Typically pink to pale pink due to trace manganese, rossmanite crystallizes in the trigonal system, has a Mohs hardness of 7–7.5, and displays a vitreous luster. It forms in highly evolved granite pegmatites, often alongside quartz, feldspar, and lepidolite, and is prized by collectors for its rarity and subtle beauty.

At the Tanco Mine in Manitoba, Canada, rossmanite occurs as part of a remarkable tourmaline sequence in the world-class LCT-type pegmatite. Here, it appears in late-stage assemblages with elbaite, marking the final phases of pegmatite crystallization. The mine’s complex zoning—from iron-rich schorl to lithium-rich elbaite and eventually rossmanite—records the chemical evolution of the pegmatite melt. This occurrence is of particular interest to mineralogists, as it represents one of the most thoroughly documented examples of rossmanite formation in a large-scale pegmatite deposit.

• Minerals: tourmaline var. rossmanite, quartz
• Locality: Tanco Mine, Bernic Lake, Manitoba, Canada
• Size: 2.5 x 1.25 x 1  inches
• Weight: 51 g