Feruvite

Feruvite is a calcic member of the tourmaline supergroup, essentially the ferrous-iron analogue of uvite (which is magnesium-dominant). It carries calcium in its X site and abundant iron in its octahedral sites, producing dark brown to black crystals. It was approved as a species in 1989.

As a calcic, iron-rich tourmaline it bridges the magnesian dravite-uvite group and the iron-rich schorl series. Crystals are typically stout prisms, opaque and dark.

Feruvite is a mineralogically important but non-gem tourmaline found mainly in calcium-rich metamorphic settings.

Feruvite forms in calcium-rich, boron-bearing metamorphic and metasomatic environments such as skarns and contact-metamorphosed limestones and dolomites. The calcium needed for the X site comes from these carbonate-rich host rocks.

Its type locality is Cuvier Island (Repanga), New Zealand. It also occurs in various skarn and altered-rock localities worldwide where iron, magnesium, calcium, and boron coexist during metamorphism.

The interplay of calcium-rich rocks and iron-bearing fluids steers tourmaline crystallization toward the feruvite composition rather than sodium-dominant species.

Feruvite appears as dark brown to black stout prismatic tourmaline crystals with rounded-triangular cross-sections and striated faces, hardness 7-7.5, vitreous luster, and no cleavage. Streak is pale.

It is visually indistinguishable from schorl, dravite, and uvite without chemistry; confirming calcium and ferrous-iron dominance requires analysis. Association with skarn and metacarbonate rocks is a strong contextual clue.

Look-alikes include schorl (sodium-dominant black), uvite (magnesium-dominant), and dark dravite; magnetite is distinguished by metallic luster and magnetism.

Feruvite has no jewelry or industrial value of note. It is collected as a systematic mineral specimen and studied for what it reveals about calcic tourmaline chemistry and skarn-forming processes.

Like other dark tourmalines it may be grouped with grounding stones in metaphysical contexts, but it is too rare and obscure to be a market item. Its real significance is scientific.