Orbicular monzodiorite (eastern Davie County, North Carolina, USA) 2 : 無料・フリー素材/写真
Orbicular monzodiorite (eastern Davie County, North Carolina, USA) 2 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Orbicular monzodiorite from North Carolina, USA (13.7 centimeters across at its widest).This attractive rock is an orbicular monzodiorite. Orbicular texture is a variety of crystalline texture and occurs in some intrusive igneous rocks. "Orbicular" refers to the subspherical structures (here colored dark green) - these are orbs, or orbicles. Such rocks are also known as "orbiculite". Orbs crystallized in the parent magma before final solidification. They usually have both concentric layering and radiating crystals. The orbs in this rock are principally composed of radiating-outward crystals of augite pyroxene and hornblende amphibole. The cores of the orbicles vary in composition, but include epidote, augite pyroxene, sphene/titanite, microcline feldspar, plagioclase feldspar, quartz, and hornblende amphibole.The light-colored, interorbicle material is a mixture of plagioclase feldspar (principally andesine) and microcline feldspar, plus minor quartz, hornblende amphibole, titanite/sphene, muscovite mica, calcite, zoisite, magnetite, and zircon. This orbicular monzodiorite apparently forms a dike or dike-like body and is intruding porphyritic biotite granodiorite country rock of the Churchland Pluton (Late Mississippian, 320 Ma). Field relations are now obscured, and the orbicular body could be a large xenolith or roof pendant.This rock has been slightly metamorphosed - the rock is partially recrystallized, the plagioclase feldspar has been saussuritized, the augite pyroxene is clouded, and some metamorphic minerals have formed (epidote, actinolite, chlorite).Location: boulder or outcrop on ~30' tall knoll just south of Rt. 64 & west of Peter Hairston Road & north-northwest of Plantation Lake (= locality of Watson, 1904, Journal of Geology 12: 294-303; = locality of Butler, 1973, Southeastern Geology 15: 127-139), west of the Yadkin River, eastern Davie County, northwest-central North Carolina, USA (vicinity of 35° 51' 56.11" North latidue, 80° 25' 03.87" West longitude)--------------------Synthesized from:Watson (1904) - Journal of Geology 12: 294-303.Butler (1973) - Southeastern Geology 15: 127-139.Samson (2001) - Geological Society of America Abstracts with Programs 33(2): 7. |
| 撮影日 | 2014-12-03 17:59:55 |
| 撮影者 | James St. John |
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