. Bulletin of the Geological Society of America. Geology. PETROLOGY 319 rieties of feldspar are present; the most abun- dant one is a polysyn- thetically twinned calcic plagioclase which occurs in small grains; the other is not twinned ex- cept occasionally on the Carlsbad law, and with its low index of refrac- tion has been identified as orthoclase. The very much clouded condition of the ground-mass from alteration products fre- quently renders the ab- solute optical indentifi- cation of the feldspars impossible. Augite, which is the most abundant mineral in the rock, appears to be identical
. Bulletin of the Geological Society of America. Geology. PETROLOGY 319 rieties of feldspar are present; the most abun- dant one is a polysyn- thetically twinned calcic plagioclase which occurs in small grains; the other is not twinned ex- cept occasionally on the Carlsbad law, and with its low index of refrac- tion has been identified as orthoclase. The very much clouded condition of the ground-mass from alteration products fre- quently renders the ab- solute optical indentifi- cation of the feldspars impossible. Augite, which is the most abundant mineral in the rock, appears to be identical with that occurring in the camp- tonite, which is de- scribed in detail below. Hornblende was not identified in any of the thin-sections. Brown biotite is an abundant constituent, strongly pleochroic (x and y = dark brown, z = yel- low), and occurs in hex- agonal .plates and irreg- ular shreds. Apatite OCCUrs in small pris- u/) Phenocrysl showing relations of analcite I in) to , - ill calcite (Ga) and ground-mans minerals (B). (Magnifies malic crystals included rion, 32 diameters.) Note iiu- well-developed crystal oul • ,, . , . lines of the analcite. The calcite is secondary, probably i" UK' principal nun- along wilh zeollte (Z) replacing analcite, which as an .,,.,1, | i -i , original constituenl occupied the entire area, erais, dux does not ap- </;l shows analcite occupying Interstices among the near fn hn oKnnrlnnf minerals of the ground-miss in the teschenite. (Magnl CO 1)0 anundant. ftcatton 00 diameters.) The analcite lias been partially nnmornna Un-hf replaced by calcite. Both (a) and (6) are typical of the numerous ngni- occur,.ence oi analcite In teschenite and : re 2. Microscopic Sketches ( Thin-sections f Teschenite illustrating occurrence of inalcite The. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectl
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1890
