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Download !GLG 101-Illustrated Vocabulary-Chapter 3 !Igneous Minerals and
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!GLG 101-Illustrated Vocabulary-Chapter 3 !Igneous Minerals and Rocks copyright 2003-Roger Weller albite *is a sodium-rich plagioclase feldspar; often white, a property from which the name is derived. -albite, cleavelandite amphibole *is a group of rock-forming silicate minerals, rich in iron, magnesium, and calcium. Cystals are often elongated. -hornblende amygdule -is a gas pocket in an igneous rock that has been filled in with a secondary mineral such as calcite or quartz. -basalt, amygdaloidal -basalt, amygdaloidal with thomsonite andesite -is a fine grained igneous rock intermediate in composition between rhyolite and basalt. It is named after its common occurrence in the Andes mountains of South America. -andesite, porphyritic apache tears -are rounded, dark, translucent obsidian nodules enclosed in perlite. These glassy nodules are often tumble polished for jewelry.. -obsidian, Apache tears -perlite and Apache tear aphanitic texture -is also known as fine grained. This igneous texture refers to very fine grained igneous rocks such as basalt and rhyolite. -basalt, fresh broken surface -rhyolite, light gray colored aplite -is a fine-grained equivalent of granite often in the form of a vein. As a granite body cools, fractures open up and the remaining magma fills these fractures, cooling relatively quickly to form the aplite veins. -aplite vein exposed on Mt.Whitney-1 -aplite vein exposed on Mt.Whitney-2 -aplite vein in decomposed granite augite -is the most common member of the pyroxene group of silicate minerals. It is usually black or blackish green in color. -augite basic igneous rock -is an igneous rock rich in dark-colored silicate minerals. -basalt, variety scoria -gabbro with labradorite basalt is a dark, fine-grained (aphanitic) volcanic rock. -basalt with olivine -basalt, variety scoria biotite -is a black mica. -biotite Bowen’s reaction series-continuous series -describes how the composition of developing feldspar crystals changes as the magma cools. The first plagioclase feldspar crystals to form at high temperatures are calciumrich (anorthite) and the last crystals to form are sodium-rich (albite). During the entire crystallization process the already formed feldspar crystals chemically react with the magma. -anorthite -labradorite -albite Bowen's reaction series-discontinuous series -is part of Bowen's Reaction series that describes the sequence in which the ferromagnesian cystallize as magma cools. The first member of the discontinuous series to for is olivine, followed by pyroxene, then amphibole, and finally biotite. -olivine -pyroxene -amphibole -biotite coarse grained -is a descriptive term for an igneous rock texture in which the mineral grains in the rock are visible to the naked eye. -rough granite -granodiorite from Mt. Whitney crystallization -is the process of disorganized atoms and molecules in a solution or melt coming together to form a solid with an organized, repeating geometrical pattern of atoms. diopside -is a green pyroxene mineral. -diopside diorite -is a coarse grained igneous rock containing mostly albite (white) feldspar and hornblende. -diorite-1 -diorite-2 -diorite-3 ferromagnesian silicate -is a silicate minerals rich in iron and magnesium, such as olivine, augite, hornblende, and biotite. -olivine -augite -hornblende -biotite fine grained -is an igneous rock texture in which the mineral grains are smaller than what the naked eye can distinguish; also called aphanitic. -basalt, fresh broken surface -rhyolite, light gray colored gabbro -is a dark, coarse grained igneous rock. -gabbro with labradorite gneiss -is a highly metamorphosed rock that is just one step away from becoming a granite. This metamorphic rock is often described as looking like a layered or lineated granite. -gneiss-1 -gneiss-2 granite -is a coarse grained igneous rock made up of feldspar, mica, and quartz. -rough granite -polished granite granodiorite -is a coarse grained igneous rock midway in composition between granite and diorite. -close up view of granodiorite on Mt. Whitney groundmass -is the mass of small crystals that surround the phenocrysts in a porphyry. hornblende -is the most common member of the amphibole family of silicate minerals. Usually hornblende forms dark brown, elongated crystals in igneous rocks such as diorite. -hornblende igneous rocks -are rocks formed as magma cools and solidifies. -black obsidian -basalt with olivine -rough granite labradorite -is a calcium-rich plagioclase feldspar, often identified by its iridescent schiller. -labradorite mafic rock -is an igneous rock rich in iron and magnesium silicates. -basalt with olivine -basalt with fresh broken surface muscovite -is also known as white mica; it is valuable because of its transparency and high electrical insulating property. -muscovite crystal -muscovite, peeling obsidian -is volcanic glass. - black obsidian-1 -black obsidian-2 -black obsidian-3 olivine -is an iron magnesium silicate that is usually yellow-green in color. This mineral is one of the first minerals to form as a basaltic magma starts to cool and crystallize. -olivine orthoclase feldspar -is a potassium feldspar. -orthoclase, salmon colored partial melting -occurs as a subducted slab of crust moves down a subduction zone. Those minerals with the lowest melting temperatures melt first. pegmatite -is a very coarse grained igneous rock. The crystals within a pegmatite are larger than one half inch. -pegmatite-1 -pegmatite-2 perlite -is a volcanic glass with high water content that is riddled with concentric cracks. -perlite and Apache tear perthitic structure -is a wood-like pattern of small, short bands of a translucent feldspar embedded in a slightly more transparent feldspar. This type of structure is often used to identify orthoclase feldspar. This structure is produced by an exsolution process as an orthoclase crystal crystallizes and then slowly cools. -perthitic structure phaneritic texture -is coarse grained, a term applied to igneous rocks whose constituent grains are large enough to see with the naked eye. -rough granite-1 -rough granite-2 phenocrysts -are the large crystals within a porphyry. -porphyry pitchstone -is a form of volcanic glass that is in the process of breaking down (devitrifying). -pitchstone-1 -pitchstone-2 plagioclase feldspars -are the calcium and sodium rich feldspars. -anorthite -labradorite -albite plagioclase twinning -On a cleavage surface of plagioclase feldspar, light is reflected off of a series of straightedged.narrow strips on cleavage surface. The cleavage surface actually consists of two slightly different crystal orientations which formed as the plagioclase crystal slowly cooled. Light is being reflected off one set of micro-cleavage surfaces from one of the crystalline orientations. If a plagioclase specimen is tipped again slightly with respect to the light source, the other set of micro-cleavage surfaces will then reflect light. -plagioclase-polysynthetic Twinning] polysynthetic twinning -See the definition for polysynthetic twinning. -plagioclase-polysynthetic twinning porphyritic texture -is an igneous rock texture that is a combination of aphanitic (fine grained) and phaneritic (coarse grained) textures. -porphyry porphyry -is an igneous rock containing two different sizes of crystals. -porphyry, rough -porphyry, cut pumice -is a very light-weight silicic volcanic rock consisting of a glass foam. Pumice is so light weight that it can float on water. -pumice, close up-1 -pumice, close up-2] -pumice, various colors pyroxene -is a group of single chain silicate minerals. Augite, a member of this silicate family of minerals, is a major constituent of basalt. -augite *[Diopside] quartz -is one of the most common minerals on the Earth, consisting of silicon and oxygen. This mineral is number 7 on Mohs sale of hardness. Quartz occurs in many different forms and may be crystalline, cryptocrystalline, or massive. -quartz, variety rock crystal -quartz, variety amethyst -quartz, variety smoky quartz rhyolite -is an aphanitic (fine grained) pastel-colored volcanic rock. -rhyolite, light gray colored -rhyolite, tan colored scoria -is a very vesicular form of basalt; dark-colored with many small gas bubble holes. -basalt, variety scoria thunderegg -is an igneous concretion, usually round, formed in conjunction with obsidian. These concretions start hollow within a obsidian flow and may either stay hollow and become geodes, or they may fill with agate or opal. The scientific term for type of structures is lithophysa (plural-lithophysae). -lithophysa-thunderegg-1 -lithophysa-thunderegg-2 ultramafic igneous rock -is made almost entirely of dark-colored iron and magnesium silicates. Peridotite is an ultramafic rock made of of olivine (peridot). vesicular basalt -is a fine grained, dark igneous rock with gas bubble holes. -basalt with fresh broken surface vesicule -is a gas bubble hole in a volcanic rock. xenolith -is a baked inclusion of country rock surrounded by an intrusive igneous rock. -xenolith from Mt. Whitney-1 -xenolith from Mt. Whitney-2
