The Educational Series of Rock Specimens, Collected and Distributed by the United States Geological Survey, Τεύχη 150-152U.S. Government Printing Office, 1898 - 400 σελίδες |
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abundant acid aggregate albite alteration analysis andesite angles apatite appears augite basalt beds biotite brown calcite carbonate of lime cement cent chemical chlorite clay cleavage color colorless composed composition conglomerate constituents contains COUNTY crossed nicols crystalline crystals dark deposited DESCRIBED BY J. S. diabase double refraction epidote eruptive extinction feldspar fragments gabbro Geological Survey glass gneiss granite granular green groundmass H₂O hand specimen hornblende hypersthene igneous rocks inclusions iron J. S. DILLER K₂O lava layers limestone magma magnetite mass material metamorphic mica microcline microscope mineral minute muscovite Na₂O nephelite nodules numerous occurs olivine oolite opaque optical original orthoclase oxide parallel particles pebbles phenocrysts plagioclase plane plates pleochroism portion prismatic prisms pyroxene quartz rhyolite sand sandstone sanidine schistose schists seen serpentine shale siliceous SiO2 sometimes Specific gravity spherulites structure substance surface thin section tion twinning U. S. Geol usually volcanic zircon
Δημοφιλή αποσπάσματα
Σελίδα 227 - Rocks, by Whitman Cross, with, a Geological Sketch of Buffalo Peaks, Colorado, by SF Emmons. 1883. 8°. 42pp. 2 pi. Price 10 cents. 2. Gold and Silver Conversion Tables, giving the coining value of troy ounces of fine metal, etc..
Σελίδα 279 - The most striking feature in the texture of the unaltered gabbro is the repeated and abrupt change in the coarseness of the grain which is seen at some localities. It was undoubtedly caused by some irregularity in the cooling of the original magma from a molten state, for which it is now difficult to find a satisfactory explanation.
Σελίδα 109 - Lepidodendron found in these concretions are equally well preserved, either in whole or in part, by horizontal cross sections. Some specimens not only show distinctly the pedicels of the sporanges and the blades in their natural position, but even sporanges with their seeds have been found in them, without perceptible alteration. In the cross section of these Lepidostrobi the sporange cells form a central row, which is surrounded by the blades in the form of a star.
Σελίδα 77 - Its economic value above ground is great, but it is greater below. In its outcrops it is a source of the finest building stone and the best grindstone grit of the country; and when it dips beneath the surface it becomes the repository of invaluable supplies of petroleum, gas and salt water.
Σελίδα 30 - The standard scale, which consists of 10 common minerals arranged in order of increasing hardness, is as follows: 1. Talc 2. Gypsum 3. Calcite 4. Fluorite 5. Apatite 6. Feldspar 7. Quartz 8. Topaz 9. Corundum 10. Diamond By using the above reference minerals, the hardness of an unknown mineral can be determined.
Σελίδα 116 - The chalk of these cliffs scales off rapidly in great conchoidal flakes, and, owing to the irregularity of this process, its face instead of being a continuous plane; is composed of many acute and reentrant angles, resembling the bastions of a fortress. The summit of the cliff is covered with gravel, but measuring from the top of the hill a short distance from the margin, the present thickness of this chalk is found to be about 135 feet from the summit to the bed underlying it.
Σελίδα 289 - This mineral shows a marked freedom from inclusions, differing in this respect from the feldspar of the hypersthene-gabbro. Wherever it comes in contact with the olivine the peculiar reactionary rims of amphibole are finely developed.1 The interior zone of these rims next to the olivine is narrow, granular, and almost colorless. Outside of this is a darker-greenish portion, having a feathery appearance. This exterior zone projects in rounded tufts into the feldspar substance, at the expense of which...
Σελίδα 378 - The coarser of these particles, like the gravel and the coarse sand, are of a compound nature, being aggregates of quartz and feldspar, with small amounts of mica and other minerals. In the finer material, on the other hand, each particle represents but a single mineral, the process of disaggregation having quite freed it from its associates, excepting, of course, in the case of microscopic inclusions, which could be liberated only by a complete disintegration of the host itself. These particles...
Σελίδα 91 - JMareau and southward across northwestern Georgia and northern Alabama, its outcrops indicating an original extent over at least 38,000 to 40,000 square miles. This shale, on account of its distinctive and striking appearance, has attracted much attention from miners and has been prospected in many places for coal and various ores. Such exploitation, however, has always been attended by failure, as the shale contains nothing of present economic importance excepting the local deposits of phosphate...
Σελίδα 296 - ... between the two minerals consisting of two parts.] The inner portion, nearest the olivine. is composed of square grains of nearly colorless pyroxene; the outer one [adjacent to the feldspar, consists] of tufts of radiating actinolite needles of a beautiful bluish-green color and strongly pleochroic. [The olivine is sometimes partly altered to serpentine.] The pyroxene constituent of the periilotite from Kings Kerry appears to be for the most part hyperstheue.