Contributions from the Geological Department of Columbia University Volume 28

Book excerpt: This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 edition. Excerpt: ... decreased solubility as determined by the slope of the solubilitysaturation curve, line AL in Figure 4. The fact that the "secondary" blebs of potash feldspar in the original member, rich in soda, are not seen, even under high magnifications (950 diameters). testifies to the nearly vertical character of the corresponding curve, BM in Figure 4. Extinction angles, crushed fragments: Popular: Microcline microperthite Technical: Microcline hypoperthite. "Orthoclase," near Unionville, Chester County, Pennsylvania. (Specimen 996.) Microscopic examination, thin section: Typical microcline microperthite with inclusions of diopside, quartz, and untwinned feldspar thought to be anorthoclase. A. Microcline microperthite (hypoperthitc), calle(l"Amazonstone," Mineral Hill, Pennsylvania. Polarized light. X30. Specimen 964. B. Microcline microperthite (hypoperthite), called "Amazonstone," near Florissant, California. Polarized light. X30. Specimen 971. Extinction angles, crushed fragments: Potash phase........ (010)........... 7.o (001)........... 17.0 Soda phase.......... (010)........... 13.0 (001)........... 1.o Inferred Composition Potash Phase Soda Phase K-feldspar........... 79.0 2.0 Na-feldspar.......... 19.0 89.0. Ca-feldspar.......... 2.0 9.0 QUANTITATIVE MICROSCOPIC ANALYSIS Phase Percentage K-feldspar Na-feldspar Ca-feldspar Silim Sodamicrocline.... 71.5 79.0 19 2.0 0. Oligoclase......... 24. 1 2.0 89 9.0 0. Quartz.................................................. 100 Sodamicrocline............... 56.5 13 1.4........ Oligoclase.....................5 21 2. 2........ Quartz......................................._........... 4.4 Total.................... 57.0 35.0 3.6 4.4 Classification: 13....