Tungstates, Molybdates – Wolframite hubnerite Composition and Structure 

Wolframite- hubnerite 
Composition. Tungstates of ferrous iron and maganese. Wolframite (Fe, Mn)WO4.

Crystallization. Monoclinic. Crystals commonly tabular parallel to the orthopinacoid, giving bladed forms. Prism zone vertically striated.

Structure. In bladed, lamellar or columnar forms. Massive granular.

Physical Properties. Perfect cleavage parallel to clinopinacoid. H. = 5-5.5. G. = 7.2-7.5. Submetallic to resinous luster. Color black in wolframite to brown in hubnerite. Streak from nearly black to brown.

Test. Fusible (3-4). Insoluble in acids. Fused with sodium carbonate, fusion then dissolved in hydrochoric acid, tin added and solution boiled gives a blue color (tungsten). Wolframite when fused with sodium carbonate in R. F. On charcoal gives a magnetic mass.

Occurrence. Comparatively rare minerals, found usually in granite and pegmatite veins, having been formed under pneumatolytic conditions. Also deposited in sulphide veins. Commonly found with cassiterite and associated also with sheelite, bismuth, quartz, pyride, galena, sphalerite, etc. Found in fine crystals from Schlaggenwald, Bohemia, and in the various tin districts of Saxony and Cornwall. Important deposits occurs in Burma, New South, Wales Bolivia. Wolframite occurs in the Black Hills, South Dakota; Boulder County, Colorado. Hubneriteis found near Silverton, Colorado; Mammoth district, Nevada; Black Hills, South Dakota.

Use. Chief ores of tungsten. Tungsten is used as as hardening metal in the manufacture of tool steel. Also as a filament in incandescent electric lights. Sodium tungstate is used in fireproofing cloth and as a mordant in dyeing.