. The prospector's field-book and guide in the search for and the easy determination of ores and other useful minerals. Sandstone. to the ocean waters where it was arrestedand became a sandstone (Fig. 2), the grains of sand arerounded, having no sharp edges as in granite. Where the sedimentary material was exceedinglydust-like, it sometimes is laid down as fine mud andfrequently in lamina, as in shale (Fig. 3). Granite is a term descriptive of rocks generally 30 prospectors field-book and guide. composed of quartz, feldspar and mica, in grains(hence the name) of a crystalline form.
. The prospector's field-book and guide in the search for and the easy determination of ores and other useful minerals. Sandstone. to the ocean waters where it was arrestedand became a sandstone (Fig. 2), the grains of sand arerounded, having no sharp edges as in granite. Where the sedimentary material was exceedinglydust-like, it sometimes is laid down as fine mud andfrequently in lamina, as in shale (Fig. 3). Granite is a term descriptive of rocks generally 30 prospectors field-book and guide. composed of quartz, feldspar and mica, in grains(hence the name) of a crystalline form. But thegranites are not all alike in the amount of either ofthe above-mentioned minerals, nor are they alike incolor. Some granites contain no mica, as in graphicgranite, only quartz and feldspar, and the quartz inthe feldspar resembling written characters. Otherscontain hornblende as well as mica, or in theplace of mica; the hornblende being in dark orblack crystalline specks, pieces, or crystals, and Fig. Shale. consisting essentially of silica, magnesia, lime, andiron. This granite is called syenite granite. Wherethe feldspar is in dictinct crystals in compact base,and sometimes lighter than the base, which is fre-quently reddish, purple, or dark green, it is a por-phyritic granite. The granites are sometimes whit-ish, grayish, or flesh-red. They are considered asmetamorphic and not igneous (Dana), althoughsome authors still consider them to be igneous-They always present a crystalline grain in varyingdegrees of fineness and prominence. One form is PREPARATORY INSTRUCTION. 31 given in Fig. 4, from a specimen in the authorspossession. This specimen contains two kinds of mica, oneblack, biotite, the other white, of silvery appearance,muscovite. The biotite presents in spots the appear-ance of hornblende, and only the pen-knife pointshows the scaly lamination of mica under the also contains crystalline forms of potash feldspar(orthoclase), distinguishable from the
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