Rutile, Octahedrite & Brookite Composition, Crystallization & Structure
Composition. Titanium dioxide, TiO2 = Oxygen 40, titanium 60. A little iron is usually present and may amount to 10 per cent.
Crystallization. Tetragonal. Usually prismatic with pyramid terminations. Vertically striated. Frequently in elbow twins, often repeated. Twinning plane is pyramid of second order. Crystals sometimes slender acicular.
Structure. Usually crystallized. Sometimes compact massive.
Physical Properties. H. = 6-6.5 G. = 4.18-4.25. Luster adamantine to submetallic. Color red, reddish brown to black. Usually nearly opaque, may be transparent.
Test. infusible. Insoluble. Fused with sodium carbonate, then fused mass dissolved in hydrochloric acid and boiled with tin, the solution assumes a violet color.
Occurrence. Rutile is found in granite, gneiss, mica schist, metamorphic limestone and dolomite, sometimes as an accessory mineral in the rock, sometimes in quartz veins traversing it. Often occurs as slender crystals penetrating quartz. Remarkable crystals come from Graves Mountain, Lincoln Country, Georgia. Also found in Alexander Country, North Carolina, and at Magnet Cove, Arkansas. Has been mined in Amherst and Nelson Counties, Virginia. Notable European localities are Kragero, Norway; Yrieix, near Limigotes, France; in Switzerland and the tyrol.
Octahedrite. Anatase
Titanium dioxide, TiO2, same as rutile and brookite. Tetragonal. Usually in pyramidal crystals, also tabular parallel to base. H. = 5.5-6. G. = 3.8-3.95. Adamantine luster. Color yellow, brown, blue, black, transparent to opaque. Tests same as for rutile 8which see). A comparatively rare mineral, found usually as an accessory mineral in metamorphic rocks, of secondary origin, having been derived from the alteration of other titanium-bearing minerals.
Brookite
Titanium dioxide, TiO2, like rutile and octahedrite. Orthorhombic. Habit varied. Tabular parallel to macropinacoid, square prismatic and at times by an equal development of 4 prism and 8 pyramid faces resembles a hexagonal pyramid. Occurs only in crystals. H. = 6. G. = 4-4.07., Luster adamantine to submetallic.
Color hair-brown to black. Translucent to opaque. Tests, same as for rutile. A rare mineral, With mode of origin and associations similar to those of octahedrite. It is apparently formed at a temperature which is lower that the formation temperature of rutile but higher than that of octahedrite. Occurs in good crystals at St. Gothard, etc., in Switzerland; in the Tyrol; Tremadoc, Wales; Ellenville, New York, Magnet Cove, Arkansas.
Mining Glossary C Assay Salting Cooling Process Importance on Mineral Formation Crusher Electrical Lockout A source of radioactivity Monoclinic System, Symmetry and Forms The Effect of Lifter Height and Drop Height on Milling and Grinding Primary Crushing Pegmatite Dikes and Veins Selecting the Primary or Jaw Crusher General Geology Anionic Agents Vanadite and Amblygonite Composition, Crystallization & Structure Sedimentary Rocks - Sandstone, Shale & Limestone Triclinic Section – Microcline Composition & Structure
