SCG.l: Granodiorite Porphyry, Sangre de Cristo Mountains, New Mexico The Sangre
ID: 115710 • Letter: S
Question
SCG.l: Granodiorite Porphyry, Sangre de Cristo Mountains, New Mexico The Sangre de Cristo Mountains in New Mexico are host to a number of granodiorite porphyry Porphyry is a textural term for an igneous rock consisting of large dispersed in a fine-grained silicate-rich, phenocrysts. If these phenocrysts are gathered in distinct or xenocryst contains minerals grained crystals (e.g.. feldspar or quartua) generally aphanitic matrix or groundmass. The larger crystals are called clusters, they are called glomerocrysts. If a phenocryst or textures which are significantly different from the bulk of the sample, then they ons of other rocks and therefore categorized as xenocrysts. Size (min)| | was! ckavasel Habit Comments Mineral Quartz Plagioclase Biotite Hornblende Color/Pleo 4es 1). Sk etch a representative example of the sample in PPL and XPL: XPL PPL 2). Characterize the grain size and mineralogy of the matrix material in this sample.Explanation / Answer
1. Quartz ( SiO2) -
size- vary in shape and size, mostly medium size ( .5 to .25 mm) color- colorless , white or tints cleavage- absent habit - prismatic crystal or massive
crystal system of quartz is hexahonal and hardness is 7 and specific gravity is 2.65
2. Plagioclase
size- medium size (.5 to .25 mm) color- usually white or grey also cololess cleavage- Perfect in two directions that intersect at approximately 90 degrees. habit - tabular
hardness of plagioclase is 6-6.5 and specific gravity is 2.55-2.65
3. Biotite ( K(Mg,Fe)3 (AlSi3O10 ) (OH)2 )
size- coarse to medium (1 to .5 mm) color- Black, dark green, dark brown cleavage- Basal, perfect habit - irregular foliated massess
hardness of the biotite is 2.5 to 3 and specific gravity is 2.8-3.2.
4. hornblend ( Ca,Na)2-3 ( Mg Fe, Al)5 Si6 (SiAl)2 O22 (OH)2
size- fine grained( .25 - .125 mm) color- green , brown or black cleavage - two direction intesecting at 56 and 156 degrees habit- massive or granular
hardness of the hornblende is 5-6 and specific gravity is 2.9 to 3.5
5. K- feldspar- KalSi308
size- medium size (.5 to .25 mm) color- white, shades of red, orange, brown or green cleavage -one perfect and other good cleavege meet at right angle habit- tabular
hardness of k-plagioclase is 6-6.5 and specific gravity is 2.55-2.65
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