Scheelite Composition, Crystallization and Structure

Composition. Calcium tungastate, CaWo4 = Tungsten trioxide 80.6, lime 19.4. molybdenum is usually present, replacing a part of the tungsten.

Crystallization. Tetragonal; tri-pyramidal. Crystals usually simple pyramids of firs order. Closely resemble isometric octahedrons in angles (Fig. 360). Faces of the pyramid of third order are small and rare.

Structure. Massive granular; in crystals.

Physical Properties. Cleavage parallel to pyramid of firs order. H. = 4.5-5. G. = 6.05 (unusually high for a mineral with nonmetallic luster). Vitreous to adamantine luster. Color white, yellow, green, brown. Usually translucent to opaque, sometimes transparent.

Test. Difficultly fusible (5). Decomposed by boiling hydrochloric acid leaving a yellow residue of tungstic oxide, which, when tin is added to the solution and boiling continued, turns first blue then brown. Recognized by its high specific gravity and the test for tungsten.

Occurrence. Formed under pneumatolytic conditions and is found in pegmatite veins or ore veins which are associated with granitic rocks. Associated with cassiterite, topaz, fluorite, apatite, molybdenite, wolframite, etc. Found at times with gold. Occurs in connection with the tin deposited of Bohemia, Saxony and Cornwall; in quantity in new South Wales and Queensland. Found in the United Estates art Trumbull, Connecticut; San Benardino County, California; near Dragoon, Cohise county, Arizona; at Leald, South Dakota; from Lealdville, Colorado.

Use. A subordinate ore of tungsten, wolframite (which see) furnishing the greater amout. Tungsten is used chiefly as a steel-hardening metal.

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