658 



UNITED STATES MINERAL RESOURCES 



iron-bearing pyroxenes at low oxygen pressures to 

 form ilmenite and iron-free pyroxene. 



Because of its strong affinity for oxygen, most of 

 the titanium in the lithosphere is in oxide minerals. 

 The three common titanium minerals are ilmenite, 

 rutile, and sphene; of these, ilmenite is by far the 

 most common, accounting for more than 90 percent 

 of the titanif erous constituents of igneous rocks. In 

 some igneous rocks where rapid crystallization has 

 occurred, the titanium has combined with magne- 

 tite to form titanium-magnetite; titanium is also 

 present in minor amounts in many other minerals. 



TITANIUM-RICH MINERALS 



Rutile is one of three titanium dioxide minerals 

 but has somewhat different physical characteristics 

 from anatase (octahedrite) and brookite, the other 

 two dioxides. Some physical characteristics of these 

 and other titanium-rich minerals are listed in table 

 139. The percentage of titanium dioxide in these 

 minerals is a measure of the percentage of titanium 

 dioxide that can be obtained in concentrates of each 

 of these minerals. Their high specific gravities indi- 

 cate that they can be separated from more common 

 light minerals by gravity methods. The indices of 

 refraction of the three varieties of titanium dioxide 

 minerals are a measure of the opacity of these 

 crystalline forms. This is of importance in their use 

 as pigments, as "covering power" of the pigment is 

 related to the opacity of its constituents. White pig- 

 ments of high opacity and high degree of chemical 

 inertness can be made from rutile and anatase. 



The principal titanium minerals form primarily 

 as products of the crystallization of igneous magmas 

 and as recrystallization products in metamorphic 

 rocks. Rutile deposits occur as local concentrations 

 in igneous and metamorphic rocks, in veins associ- 

 ated with igneous and metamorphic rocks, and as 

 concentrations in sedimentary rocks and unconsoli- 

 dated sediments derived from the weathering of 

 rutile-bearing rocks. 



PRIMARY RUTILE DEPOSITS 



Rutile occurs primarily in alkalic igneous rocks, 



in alkalic noritic-anorthositic complexes, and in gra- 

 nitic and syenitic veins and pegmatites. It is also 

 formed in aluminum-rich high-grade metamorphic 

 rocks and in high- and low-grade metamorphosed 

 mafic and ultramafic rocks. All economic primary 

 rutile deposits are in the noritic-anorthositic com- 

 plexes. Few primary rutile deposits are of economic 

 value, however, and most primary rutile is recov- 

 ered as a product of ilmenite mining. 



At Kragero, Norway, rutile occurs in an aplite 

 dike associated with gabbro that contains an aver- 

 age of 5-10 percent rutile. In the United States, in 

 Amherst and Nelson Counties, Va. (Hillhouse, 1960; 

 Ross, 1941), rutile occurs as an abundant mineral 

 in dikelike or lenticular bodies of nelsonite, an 

 ilmenite-apatite-rutile-rich rock, associated with 

 a larger body of anorthosite. Some of the nelsonite 

 contains as much as 60 percent rutile. Rutile also 

 occurs in the anorthosite as disseminated grains 

 averaging 4-5 percent of the rock and in quartz- 

 rutile stringers containing as much as 30 percent 

 rutile. Rutile has been mined from nelsonite dikes 

 adjacent to, and disseminations in, anorthosite at 

 Roseland, Va. (Peterson, 1966). It has also been 

 produced from an alkalic igneous complex at Mag- 

 net Cove, Ark. ( Fryklund and Holbrook, 1950). In 

 the Magnet Cove area, rutile and brookite occur in 

 association with novaculite and aegirine phonolite 

 porphyry. The rutile in that area is in carbonate- 

 feldspar veins that cut the porphyry, and the brook- 

 ite occurs as crystals in quartzite masses embedded 

 in the novaculite. Chloritic ultramafic rock in Har- 

 ford County, Md., contains about 5 percent rutile in 

 association with abundant magnetite, apatite, and 

 ilmenite, on the flank of a serpentinized ultramafic 

 body (Herz and Valentine, 1970). 



In Mexico, rutile is associated with anorthosite at 

 Pluma Hidalgo, Oaxaca (Roy, 1970a) ; and in 

 Canada, rutile occurs in ilmenite-rich anorthosite 

 in the St. Urbain area, Quebec (Rose, 1969). 



Potentially economic deposits of rutile occur near 

 Evergreen in the Front Range of Colorado as fine 

 disseminations in fluorine-metasomatized light- 



Table 139 — Princi'pal titanium-rich minerals 



Anatase TiO- 



Brookite TiO. 



Rutile Ti0= 



Ilmenite FeTiOa 



Perovskite CaTiOc 



Sphene CaTiSiOs 



100 



100 



100 



52.7 



58.9 



40.8 



98.2 

 98.8 

 45.7 

 46.2 

 38.7 



3.90 



4.14 

 4.21 

 4.72 

 4.01 



2.488-2.561 

 2.583-2.700 

 2.612-2.899 



2.¥0-2~.37"" 



1.900-2.034 



Tetragonal. 



Orthorhombic. 



Tetragonal. 



Hexagonal. 



( Pseudoisometric, 



monoclinic?) 

 Monoclinic. 



