Post by shivan on Dec 30, 2014 13:47:06 GMT 10
G'day all, a few more rocks from the photographic collection
Dolerite- Medium grained mafic rock composed mostly of plagioclase and clinopyroxene (augite). It formed in a small intrusion, probably at shallow crustal level. This rock has experienced very low grade metamorphism and plagioclase and augite are partly altered. Magnetic susceptibility 4340 x 10^-5
Porphyritic dacite- Contains phenocrysts of plagioclase, quartz and hornblende in a fine grained groundmass of alkali feldspars and quartz. Could have formed in a thick lava flow or shallow intrusion. Magnetic susceptibility 15 x 10^-5 SI
Rhyolite obsidian- This is volcanic glass of rhyolite composition and it has no crystals. Flow banding is apparent. It formed as part of a lava flow or lava dome. Magnetic susceptibility 61 x 10^-5 SI
Rhyolite ignimbrite- Contains scattered crystals (K-feldspar, quartz) and flattened and altered pumice fragments in a fine grained groundmass of alkali feldspar and quartz that represents devitrified volcanic ash. Flow foliation is apparent. This rock was emplaced as a hot pyroclastic flow. Magnetic susceptibility 195 x 10^-5 SI
Komatiite- This rock is the volcanic extrusive equivalent of peridotite and was originally composed of bladed olivine crystals, minor clinopyroxene and glass. It has been metamorphosed and the igneous minerals were replaced by amphibole, chlorite and magnetite. This rock initially formed in a submarine lava flow. Magnetic susceptibility 9340 x 10^-5 SI
Monzonite- Coarse grained, porphyritic intermediate to felsic rock, containing abundant plagioclase, pink K-feldspar (some as phenocrysts) and hornblende, with minor quartz and biotite. It forms a plutonic body> This is an I-type rock (formed from igneous rock as oppose to S-type sedimentary). Magnetic susceptibility 90 x 10^-5 SI
Pyroxenite- Coarse grained ultramafic rock consisting of abundant orthopyroxene and minor plagioclase. It has formed in the lower part of a layered mafic-ultramafic intrusion. Magnetic susceptibility 65 x 10^-5 SI
Gabbro- Coarse grained mafic rock composed of abunsant plagioclase, with subordinate amounts of clinopyroxene (augite:black), orthopyroxene (dark brown) and olivine, This rock has formed in a possibly layered mafic intrusion. Magnetic susceptibility 315 x 10^-5 SI
Peridotite- Coarse grained ultramafic rock consisting of abundant olivine, minor orthopyroxene (dark brown), clinopyroxene (dark green) and little chromite (black). This rock is representative of parts of the earths mantle and has been brought to the earths surface entrained in the eruption of a basalt volcano. Peridotite is typically serpentinised (i.e serpentinite). magnetic susceptibility 45 x 10^-5 SI
Diorite- Medium to coarse grained intermediate rock composed of abundant plagioclase, biotite and hornblende. It forms a plutonic body. Magnetic susceptibility 78 x 10^-5 SI
Monzogranite (Itype)- Coarse grained, leucocratic, weakly porphyritic felsic rock, containing abundant pink K-feldspar (some as phenocrystss), quartz, with less common plagioclase and biotite. Forms a large plutonic body. Many I-type granitoids contain pink feldspar (because Al or Ti rich). Magnetic susceptibility 188 x 10^-5 SI
Granodiorite (S-type)- Coarse grained, felsic rock, containing abundant plagioclase, quartz and biotite, with minor K-feldspar. Forms a large plutonic body. S-type granitoids are typically grey in colour. Magnetic susceptibility 22 x 10^-5 SI
Porphyritic micromonzogranite ("granitic porphyry")- Strongly porphyritic felsic rock, with abundant K-feldspar phenocrysts and less common phenocrysts of quartz and hornblende (partly altered), in a fine to medium grained groundmass containing abundant feldspar and quartz. May form a small intrusion or represent the marginal phase of a large plutonic body. This is an I-type rock. Magnetic susceptibility 57 x 10^-5 SI
Lamprophyre- Medium grained intermediate igneous rock, typically containing small phenocrysts of ferromagnesian minerals ( in this case, biotite), in a groundmass rich in feldspars (in this case K-feldspar). Lamprophyres are typically emplaced as dykes and have a mantle source. They are characteristic of orogenic belts and in places found in association with structurally-controlled (orogenic) vein gold deposits. Magnetic susceptibility 38 x 10^-5 SI
Microgranite ("aplite")- Fine to medium grained leucocratic felsic igneous rock, composed of abundant K-feldspar and quartz, with trace biotite. Could form a small intrusion at the roof or margin of a large leucogranite body. Magnetic susceptibility 3 x 10^-5 SI
Granite pegmatite- Very coarse grained leucocratic granitic rock composed mostly of quartz and K-feldspar, with minor tourmaline. This rock has formed as a small intrusion at the margin of a larger granitic pluton. Magnetic susceptibility 5 x 10^-5 SI
Weakly porphyritic olivine basalt- This rock contains a few olivine phenocrysts, but is mostly composed of a fine grained mass of plagioclase, clinopyroxene, olivine and magnetite. It represents part of a lava flow and has a few olivine-rich peridotite mantle-derived xenoliths. Magnetic susceptibility 2780 x 10^-5 SI
Trachyte- Displays scattered phenocrysts of alkali (Na-K) feldspar in a fine grained groundmass of alkali feldspar and minro clinopyroxene. It represents part of a thick lava flow. Magnetic susceptibility 380 x 10^-5 SI
Porphyritic andesite- This rock contains abundant plagioclase phenocrysts and a few small clinopyroxene phenocrysts in a fine grained feldspathic groundmass. It represents part of a lava flow. Magnetic susceptibility 1590 x 10^-5 SI
Porphyritic basalt- This rock contains large plagioclase phenocrysts in a fine grained groundmass of plagioclase, clinopyroxene and olivine. It forms a thick lava flow. Magnetic susceptibility 370 x 10^-5 SI
Porphyritic rhyolite- Contains phenocrysts of K-feldspar and quartz in a fine grained groundmass of alkali feldspar and quartz. Could have formed in a thick lava flow or shallow intrusion. Magnetic susceptibility 195 x 10^-5 SI.
Dolerite- Medium grained mafic rock composed mostly of plagioclase and clinopyroxene (augite). It formed in a small intrusion, probably at shallow crustal level. This rock has experienced very low grade metamorphism and plagioclase and augite are partly altered. Magnetic susceptibility 4340 x 10^-5
Porphyritic dacite- Contains phenocrysts of plagioclase, quartz and hornblende in a fine grained groundmass of alkali feldspars and quartz. Could have formed in a thick lava flow or shallow intrusion. Magnetic susceptibility 15 x 10^-5 SI
Rhyolite obsidian- This is volcanic glass of rhyolite composition and it has no crystals. Flow banding is apparent. It formed as part of a lava flow or lava dome. Magnetic susceptibility 61 x 10^-5 SI
Rhyolite ignimbrite- Contains scattered crystals (K-feldspar, quartz) and flattened and altered pumice fragments in a fine grained groundmass of alkali feldspar and quartz that represents devitrified volcanic ash. Flow foliation is apparent. This rock was emplaced as a hot pyroclastic flow. Magnetic susceptibility 195 x 10^-5 SI
Komatiite- This rock is the volcanic extrusive equivalent of peridotite and was originally composed of bladed olivine crystals, minor clinopyroxene and glass. It has been metamorphosed and the igneous minerals were replaced by amphibole, chlorite and magnetite. This rock initially formed in a submarine lava flow. Magnetic susceptibility 9340 x 10^-5 SI
Monzonite- Coarse grained, porphyritic intermediate to felsic rock, containing abundant plagioclase, pink K-feldspar (some as phenocrysts) and hornblende, with minor quartz and biotite. It forms a plutonic body> This is an I-type rock (formed from igneous rock as oppose to S-type sedimentary). Magnetic susceptibility 90 x 10^-5 SI
Pyroxenite- Coarse grained ultramafic rock consisting of abundant orthopyroxene and minor plagioclase. It has formed in the lower part of a layered mafic-ultramafic intrusion. Magnetic susceptibility 65 x 10^-5 SI
Gabbro- Coarse grained mafic rock composed of abunsant plagioclase, with subordinate amounts of clinopyroxene (augite:black), orthopyroxene (dark brown) and olivine, This rock has formed in a possibly layered mafic intrusion. Magnetic susceptibility 315 x 10^-5 SI
Peridotite- Coarse grained ultramafic rock consisting of abundant olivine, minor orthopyroxene (dark brown), clinopyroxene (dark green) and little chromite (black). This rock is representative of parts of the earths mantle and has been brought to the earths surface entrained in the eruption of a basalt volcano. Peridotite is typically serpentinised (i.e serpentinite). magnetic susceptibility 45 x 10^-5 SI
Diorite- Medium to coarse grained intermediate rock composed of abundant plagioclase, biotite and hornblende. It forms a plutonic body. Magnetic susceptibility 78 x 10^-5 SI
Monzogranite (Itype)- Coarse grained, leucocratic, weakly porphyritic felsic rock, containing abundant pink K-feldspar (some as phenocrystss), quartz, with less common plagioclase and biotite. Forms a large plutonic body. Many I-type granitoids contain pink feldspar (because Al or Ti rich). Magnetic susceptibility 188 x 10^-5 SI
Granodiorite (S-type)- Coarse grained, felsic rock, containing abundant plagioclase, quartz and biotite, with minor K-feldspar. Forms a large plutonic body. S-type granitoids are typically grey in colour. Magnetic susceptibility 22 x 10^-5 SI
Porphyritic micromonzogranite ("granitic porphyry")- Strongly porphyritic felsic rock, with abundant K-feldspar phenocrysts and less common phenocrysts of quartz and hornblende (partly altered), in a fine to medium grained groundmass containing abundant feldspar and quartz. May form a small intrusion or represent the marginal phase of a large plutonic body. This is an I-type rock. Magnetic susceptibility 57 x 10^-5 SI
Lamprophyre- Medium grained intermediate igneous rock, typically containing small phenocrysts of ferromagnesian minerals ( in this case, biotite), in a groundmass rich in feldspars (in this case K-feldspar). Lamprophyres are typically emplaced as dykes and have a mantle source. They are characteristic of orogenic belts and in places found in association with structurally-controlled (orogenic) vein gold deposits. Magnetic susceptibility 38 x 10^-5 SI
Microgranite ("aplite")- Fine to medium grained leucocratic felsic igneous rock, composed of abundant K-feldspar and quartz, with trace biotite. Could form a small intrusion at the roof or margin of a large leucogranite body. Magnetic susceptibility 3 x 10^-5 SI
Granite pegmatite- Very coarse grained leucocratic granitic rock composed mostly of quartz and K-feldspar, with minor tourmaline. This rock has formed as a small intrusion at the margin of a larger granitic pluton. Magnetic susceptibility 5 x 10^-5 SI
Weakly porphyritic olivine basalt- This rock contains a few olivine phenocrysts, but is mostly composed of a fine grained mass of plagioclase, clinopyroxene, olivine and magnetite. It represents part of a lava flow and has a few olivine-rich peridotite mantle-derived xenoliths. Magnetic susceptibility 2780 x 10^-5 SI
Trachyte- Displays scattered phenocrysts of alkali (Na-K) feldspar in a fine grained groundmass of alkali feldspar and minro clinopyroxene. It represents part of a thick lava flow. Magnetic susceptibility 380 x 10^-5 SI
Porphyritic andesite- This rock contains abundant plagioclase phenocrysts and a few small clinopyroxene phenocrysts in a fine grained feldspathic groundmass. It represents part of a lava flow. Magnetic susceptibility 1590 x 10^-5 SI
Porphyritic basalt- This rock contains large plagioclase phenocrysts in a fine grained groundmass of plagioclase, clinopyroxene and olivine. It forms a thick lava flow. Magnetic susceptibility 370 x 10^-5 SI
Porphyritic rhyolite- Contains phenocrysts of K-feldspar and quartz in a fine grained groundmass of alkali feldspar and quartz. Could have formed in a thick lava flow or shallow intrusion. Magnetic susceptibility 195 x 10^-5 SI.