ON AN OCCURRENCE OF CORUNDUM AND DUMORTI- 
ERITE IN PEGMATITE IN COLORADO 
GEORGE I. FINLAY 
Colorado Springs, Colo. 
Introductory.—The purpose of the writer in the present paper is to 
record the occurrence of corundum in association with dumortierite 
and sillimanite in the réle of igneous minerals in pegmatite, near 
Canyon City, Colo. The pegmatite dike in question is acid, its 
mineralogy is that of a granite, and it stands in epidote schist near 
masses of granite along Grape Creek. Corundum was first noted in 
the dike by Mr. Eugene Weston, of Canyon City. The occurrence 
is recorded by J. Hl. Pratt in the paper cited below.’ Vhe facts 
point to the igneous character of the pegmatite dike. It is therefore 
of interest to find corundum, dumortierite, and sillimanite in it as 
possible original constituents of such an acid rock. The dike does 
not show signs of metamorphism. 
The complex of rocks appearing at the north end of the Wet 
Mountains in Colorado, on which the Ordovician and later Paleozoic 
series rests unconformably, consists largely of schist and gneiss, cut 
by veins of pegmatite and by diabase dikes. The wall rock in 
which the corundum-bearing pegmatite vein stands is dark, fine- 
grained schist. Under the microscope apple-green pleochroic horn- 
blende appears as the most abundant constituent. Quartz is in 
small grains. The feldspar is deeply kaolinized, with muscovite as 
an alteration product. Epidote and magnetite are abundant. Apa- 
tite and hematite occur sparingly. Dark biotitic granite appears in 
extensive masses near the locality in question. Microcline, acid 
plagioclase, quartz, and biotite, with zircon, apatite, magnetite, and 
secondary hematite, are its constituent minerals. 
_ Occurrence in the field—The vein of pegmatite is seen on the 
ridge between the Rocky Mountain Boy and Joker claims on Grape 
tJ. H. Pratt, ‘‘Mineral Resources, Abrasives,” U. S. Geological Survey, 1901, 
p- 45; see also North Carolina Geological Survey, Vol. I (1905), p. 238. 
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