#volcano
All of these samples were collected at Hogen Camp Mine, Harriman State Park, NY. The first image is a reflected light image of the ore vein. The ore vein formed as a result of dextral shear which ultimately created large fractures. Shortly after this, hydrothemal alteraltion occured of the metavolcanic gneiss in the region (image 2 and 3). The metavolcanic gneiss is rich in iron. Due to this, the highly acidic metamorphic fluids began to precipitate in the fractures. The process yeilded magnetite, clinopyroxene, and less common biotite within the fractures occuring at Hogen Camp Mine. The clinopyroxene and biotite are highly rich in iron.
Image 3 and 4 is the local pink pegmatites that occured in the region around 923 Ma. The pegmatitic dikes formed post-Ottawan orogeny. Composition includes: alkali feldspar with minor constituents of clinopyroxene and quartz.
This rock is a quartzofeldspathic gneiss from Surebridge Mine in Harriman State Park, NY. What’s so cool about this is you can see the hydrothermal process which alters biotite to chlorite. The large brown grain being biotite, and the purple/blue/green in the center being chlorite. (10x XPL)
Alkali Feldspar crystals are large in this thin section. The alkali feldspar have subhedral crystals. The quartzy matrix in some areas is intergrown at the edge of the alkali feldspar crystal faces. The muscovite crystallized in the interstitial space and have anhedral crystal faces. To differentiate between the muscovite and the biotite pleochroism comes into effect. The biotite is darker amber under PPL and muscovite is tan/light brown. Both are pleochroic under PPL.
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This rock is composed predominantly of plagioclase feldspar that are large euhedral crystals suggesting that they formed first in the melt. In the interstitial space there is clinopyroxene which suggests that the clinopyroxene formed after the plagioclase. The larger crystals do not have any form of twinning, so at first glance they look like quartz. After using the bertrand lens, the big crystals have an optic sign of biaxial which help conclude that the crystals are plagioclase and not quartz. The fractures in the big crystals have clinopyroxene crystals present. The rock is most likely an anorthosite/tonalite.
(For future posts #optmin is the tag to see all my original content!)
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The plagioclase in this thin section has polysynthetic twinning. The orthopyroxene also has twinning present in most grains. The clinopyroxene is filling voids in the rock and have an anhedral structure, filling interstitial space, compared to to the plagioclase and orthopyroxene which range from subhedral to euhedral. The rock is a gabbronorite due to the presence of both orthopyroxene and clinopyroxene.
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This rock is predominantly composed of quartz, alkali feldspar, and plagioclase. The alkali feldspar grains are large and take up a decent amount of the slide. The perthite is mainly one grain that is large and is about 11mm. The plagioclase has
polysynthetic twinning.The muscovite is pleochroic under PPL and has clinopyroxene embayed in the core. Clinopyroxene is present because the melt reacted with the clinopyroxene and create muscovite. Leucite is also present in a minimal quantity. The leucite is embayed in the alkali feldspar. This happened when the alkali feldspar started to crystalize. The silica content was too great and the leucite reacted with the melt to form alkali feldspar. Due to the composition the rock would just be classified as a granite.
(leucite in 2nd pic)
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Composition includes: biotite, muscovite, chlorite, feldspars, oxides, and quartz. Feldspar poikiloblasts with inclusions of quartz and oxides are prominent throughout much of the sample. Most poikiloblasts occurred synkinematic to the 1st deformation event (D1) and rotation occurred. D1 had a direct effect on the foliation (S1) of minerals that already crystallized. D2 led to crystallization of quartz which is seen in quartz ribbons and pressure fringes throughout the sample.
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This thin section shows an amygdule in a sample of amygdaloid basalt. The rock formed due to an eruption of gaseous, low viscous magma which resulted in vesicles throughout much of the rock. The rock then underwent hydrothermal alteration and low temperature alteration minerals formed in the once vesicles, forming amygdules. The amygdules are composed of quartz, celadonite (a type of mica) and epidote.
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Websterite in thin section
Clinopyroxene and orthopyroxene with few anhedral plagioclase crystals in interstitial space. Opaques (oxides) also present.
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The largest volcano in the solar system, located on Jupiter’s moon Io, is called Loki, named after Loki of Norse Mythology. There are several other volcanoes on the moon of Io, and all of them are named after mythical figures, most of whom are associated with fire.
Loki generates more lava and heat than all volcanoes on Earth combined, is 202km in diameter, and under the crust, is part of a molten core as large as half of the Earth’s moon.
Above, Loki’s eruption is clearly visible from space.
(Information gathered from the Smithsonian National Air and Space Museum’s website, located at: http://airandspace.si.edu/ , originally obtained via NASA’s Galileo Mission: http://solarsystem.nasa.gov/galileo/)
