KYANITE AND RELATED MINERALS 



309 



40 percent, but generally is less than 15 percent. 

 Their distribution may be very irregular because of 

 variable alumina content of the original beds or 

 layers and the subsequent strong deformation of 

 the layered rock. Usually only one of the AUSiOj 

 minerals is present, but two of them occur together 

 at some places, and all three have been found to- 

 gether at a few places. 



Another important but less common type of de- 

 posit consists of quartzose rock that contains one or 

 more of the kyanite-group minerals in association 

 with various other aluminous minerals and quartz. 

 These quartzose deposits generally have a higher 

 content of AUSiOs minerals (commonly more than 

 20 percent) than do the micaceous schists and 

 gneisses, but they are much smaller in size. Kyanite 

 is usually more abundant in the quartzose deposits 

 than are other minerals of the group. 



The kyanite-group minerals also occur in quartz 

 veins and pegmatites but in relatively small amounts. 

 These minerals are very resistant to weathering 

 and erosion and may accumulate in abundance in 

 the soils overlying the source rocks. Subsequently, 

 the AlaSiOs minerals are concentrated in stream and 

 river alluvium ; later in the cycle of sediment trans- 

 port, they may be preserved in beach sands along 

 with other resistant minerals such as quartz, zircon, 

 monazite, staurolite, and the titanium minerals 

 ilmenite and rutile. 



RESOURCES 



UNITED STATES RESOURCES OF KYANITE- 

 GROUP MINERALS 



The AlsSiOs minerals occur in nearly every large 

 area of metamorphic rocks in the country (Espen- 

 shade, 1961, 1962 ; Varley, 1965) . The kyanite-group 

 minerals have been found in bedrock at innumerable 

 places in at least 30 States (Grametbauer, 1959) . At 

 many places, no more than a few percent of these 

 minerals is contained in the rock, too little to be of 

 economic interest. Only those deposits that contain 

 at least 10 percent of the AUSiOs minerals are of 

 potential economic value. All domestic resources are 

 of the disseminated type of ore in which the kyanite 

 minerals must be separated from quartz, mica, and 

 other minerals by beneficiation. 



Domestic resources of the kyanite-group minerals 

 are summarized in table 62 according to three types 

 of deposits. Enormous amounts of the AUSiOs min- 

 erals are contained in micaceous schists and gneiss, 

 but such deposits typically have lower contents of 

 these minerals than do the quartzose deposits and 

 have produced only a few percent of the total do- 



Table 62. — United States resources of kyanite and related 

 minerals 



[Short tons of contained kyanite-group minerals] 



^ Identified resources : Specific, identified mineral deposits that may or 

 may not be eva uated as to extent and grade, and whose contained min- 

 rals may or may not be profitably recoverable with existing technology 

 and economic conditions. 



2 Hypothetical resources: Undiscovered mineral deposits, whether of 

 recoverable or subeconomic grade, that are geologically predictable as exist- 

 ing in known districts. 



mestic output of these minerals. Probably at least 

 95 percent of total production has come from quartz- 

 ose deposits, although these deposits contain no 

 more than 5 percent of our resources. 



The data used in estimating these resources are 

 generally better for the quartzose deposits and by- 

 product sources than for the deposits of micaceous 

 schist and gneiss. For identified resources, the 

 minimum grade (except for byproduct sources) has 

 been taken as 10 percent content of kyanite-group 

 minerals ; estimates of open-cut mining depths range 

 from 50 feet to several hundred feet. Estimates of 

 hypothetical resources are based on extensions of 

 known deposits or districts in depth or in area. None 

 of the micaceous schist and gneiss deposits included 

 in table 62 is now being mined, but profitable min- 

 ing of some may become possible within the next 

 25 years. Deposits of sillimanite schist containing 

 finely fibrous sillimanite ("fibrolite") are not in- 

 cluded in the resource estimate because of the 

 difficulty in making a clean and efficient separation 

 of this variety of sillimanite. 



DEPOSITS OF MICACEOUS SCHIST AND GNEISS 



Kyanite and sillimanite are widely distributed in 

 micaceous schist and gneiss in the Appalachian 

 mountain system from Maine to Alabama. Andalu- 

 site in such rocks is much more restricted in occur- 

 rence and is found principally in New England. Gen- 

 eral distribution of the AlaSiOs minerals in the 

 Appalachians was shown on a map by Morgan 

 (1972) ; distribution in New England has also been 

 given (Doll and others, 1961; Hussey and others, 

 1967 ; and Thompson and Norton, 1968) ; distribu- 

 tion in parts of the southern Appalachians was 

 given by Overstreet and others (1968), Carpenter 

 (1970), and Hadley and Nelson (1971). The principal 

 Appalachian deposits of micaceous schist and gneiss 

 included in table 62 are kyanite-garnet-mica 

 gneisses near New Hartford, Conn. (R. W. Schnabel, 

 written commun., Apr. 1972) ; similar gneiss and 



