Mineral Compositions of Selected Granites and Gneisses of New England
Infrared absorption spectrophotometry (4000 to 300 cm −1 ) and ultraviolet emission spectrography (2300 to 3500 A) were employed in order to obtain semiquantitative compositional data for certain minerals from selected granites and gneisses of New England. The minerals separated from each of 49 representative rock samples (when practical) included: essential quartz, potassic feldspar, plagioclase, biotite, and accessory magnetite. The rock units (or subunits) and number of samples were: Conway and equivalent(?) granites, 14; Westerly granite, 3; Middle-town and Monson gneisses, 10; Glastonbury and Maromas gneisses, 7; Stoney Creek, Clinton, and Sterling granitic gneisses, 8; and Canterbury gneiss, 7. The minor and trace elements included: Ag, Ba, Be, Ca, Cu, Ga, Mn, Pb, Sn, Ti, and Zr. Major element data, as interpreted from the infrared spectra, included: (1) obliquity and perthitic nature of potassic feldspar; (2) general composition (An 10 to An 33 ) and/or order-disorder of plagioclase; (3) Fe:Mg ratio and tetrahedral Al(?) of biotite; and (4) ilmenite (or hematite) percentage in magnetite. Quartz showed no spectral variation. The primary purpose of this preliminary reconnaissance survey, employing this instrumental approach, was to determine if some of the data obtained would be consistent and systematically related to specific rock units. It is concluded that this has been demonstrated, and the indicative data have been emphasized.