Transactions . Fig. 8.—Nodular chrome ore, Briggs Creek, Oregon. Interstices be-tween nodules of chromite are filled with bright green and yellowishserpentine, from pyroxene and olivine, a vein of serpentine cuts thechromite nodules and also the interstitial serpentine. size. J. S. DILLEIt 115 veins of serpentine. The original silicates, chiefly olivine, from whichthe serpentine is derived, appear to have enveloped the chromite nodulesas if the chromite were formed before the silicates. Fig. 9 represents nodular ore in which the nodules of chromite (4 to10 mm. in diameter) are wholly
Transactions . Fig. 8.—Nodular chrome ore, Briggs Creek, Oregon. Interstices be-tween nodules of chromite are filled with bright green and yellowishserpentine, from pyroxene and olivine, a vein of serpentine cuts thechromite nodules and also the interstitial serpentine. size. J. S. DILLEIt 115 veins of serpentine. The original silicates, chiefly olivine, from whichthe serpentine is derived, appear to have enveloped the chromite nodulesas if the chromite were formed before the silicates. Fig. 9 represents nodular ore in which the nodules of chromite (4 to10 mm. in diameter) are wholly crystalline and apparently uniformthroughout each nodule, although there is considerable variation in theluster of the grains, which appear on the polished surfaces of the may be due to difference in chemical composition or more likely tothe different angle of the crystal section. The nodules are much frac-tured, and the fissures, as well as the internodular spaces, arc filled with. Fig. 9.—Nodular chrome ore, Placer mine, Eldorado Co., Calif. Chromite(black) enclosed by tremolite (white). The chromite grains are cut by VlilNS OF serpentine AND TREMOLITE, WHICH REPRESENT EARLIER SILICATES Natural size. a greenish-white mineral, the acicular crj^stals of which locally have aradial fibrous arrangement; W. T. Schaller identifies this as tremo-lite, which readily alters to serpentine, with which it is a thin section, the clear, acicular crystals have the distinct cleavageof hornblende, and their occurrence in veins cutting the nodules of chro-mite shows that the tremolite is secondary. In this respect it is likethe serpentine with which it is associated; both form veins in the original silicate from which the tremolite is derived was probablypyroxene. Judging from the structure, the primary silicates appear tobe younger than the chromite nodules, which they enclose. In one 116 UKCKNT sriJDllOS OK DOMIOSIlC ( ; i)i:i()siTs part o
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