Wolframite

Wolframite is the traditional chief ore of tungsten, an iron manganese tungstate that forms a solid-solution series between iron-rich ferberite and manganese-rich hübnerite. It crystallizes in the monoclinic system, typically as thick tabular or bladed crystals with a brownish-black to iron-black color and a submetallic to resinous luster.

It is notably dense and heavy because of its tungsten content, and shows one direction of perfect cleavage that produces flat, shiny surfaces. The streak ranges from brownish-black to nearly black depending on composition.

Wolframite supplied most of the world's tungsten through the twentieth century and remains a key strategic ore, the source of the extraordinarily hard, high-melting metal used in tools and armaments.

Wolframite forms in high-temperature hydrothermal environments, concentrating in quartz veins, greisens, and pegmatites associated with granitic intrusions. It commonly occurs with cassiterite (tin oxide), making many deposits combined tin-tungsten ores, alongside quartz, mica, topaz, fluorite, and arsenopyrite.

Because it is hard and dense, wolframite also accumulates in placer (stream) deposits where it weathers from veins. Major producing regions include the tin-tungsten belt of southern China (the world's dominant source), Bolivia, Portugal (Panasqueira), Cornwall in England, Myanmar, and Rwanda and the Democratic Republic of Congo, where it is one of the "conflict mineral" 3T ores.

Wolframite is identified by its brownish-black to iron-black color, submetallic to resinous luster, bladed or tabular crystal habit, one perfect cleavage, and a brownish-black streak. Its standout property is high density — it feels surprisingly heavy in the hand.

Hardness is moderate at 4-4.5. Look-alikes include columbite-tantalite (also dark and heavy, distinguished by chemistry), ilmenite, and black tourmaline (much lighter and harder). The combination of great weight, bladed habit, single perfect cleavage, and association with quartz veins and cassiterite usually pins down wolframite.

Wolframite is a principal ore of tungsten, the metal valued for the highest melting point of all metals and for forming tungsten carbide, one of the hardest manufactured materials. Tungsten and its carbide go into cutting tools, drill bits, mining and machining equipment, wear-resistant parts, and armor-piercing projectiles.

Tungsten also makes lamp filaments and heavy alloys for radiation shielding and balance weights. Wolframite is one of the "3T" conflict minerals (tin, tantalum, tungsten) subject to responsible-sourcing scrutiny. It has no gemstone use, though crystallized specimens are collected.