Minerals in this rock include quartz, plagioclase, biotite, and K-feldspar.
Micrographic quartz and K-feldspar (cuneiform shaped intergrowths) dominate this rock.
This crystal-rich rhyolite contains phenocrysts of quartz, K- feldspar (sanidine), plagioclase, and biotite in a fine-grained groundmass. Note the interesting shape of the (partially resorbed) quartz grain in the center of the photograph.
This rock contains hornblende, plagioclase clinopyroxene, biotite, and quartz. Notice how the hornblende rims the small core of relict clinopyroxene in the center of this photo, indicating a reaction relationship.
A diabase is a mafic rock with grain size more or less transitional between gabbro (coarse) and basalt (fine). Notice the elongate lath-shaped plagioclase and the colorful clinopyroxene and possible olivine in this rock.
Plagioclase and hypersthene (orthopyroxene) dominate this rock. This slide may have been cut a little too thick, accounting for the higher-than- expected interference colors of the hypersthene.
A norite is a gabbro in which the pyroxene is principally orthopyroxene. This norite from the uppermost portions of the famous Stillwater Complex in Montana also contains some clinopyroxene. Generally, clinopyroxene has higher interference colors than orthopyroxene, as shown in this photomicrograph.
This rock is composed almost entirely of albitic plagioclase.
This rock is dominated by the clinopyroxene augite.
Bronzitite is an orthopyroxenite dominated by the mineral hypersthene. Almost all of the grains in this photomicrograph are hypersthene. This rock also contains some interstitial plagioclase better seen in plane light.
Almost all of the grains in this rock are olivine. Note the high order interference colors of olivine and the minor secondary calcite which occurs as veinlets through the sample.
Thin sections of foyaite, a nepheline syenite, with some plagioclase, microcline and nepheline
Thin section of syenite., with some plagioclase and clinopyroxene, but also biotite and heavy residua of K- Feldspar. This is presumably a plag-rich syenite.
The light gray streaks in this photomicrograph are plagioclase exsolution lamellae in gray K-feldspar. Perthite forms as an originally homogeneous feldspar exsolves two feldspars as temperature falls below the feldspar solvus during subsolidus cooling.
Myrmekitic texture defined by wormy (rounded) intergrowths of quartz and K-feldspar in plagioclase. Probably forms as a result of subsolidus exchange. Compare this texture to micrographic texture.
This breccia is composed of fragments of a variety of volcanic materials.
Komatiites are rare ultramafic volcanic rocks. This sample displays the characteristic "spinifex texture" defined by extremely acicular olivine phenocrysts--probably a sign of rapid crystallization from a significantly-undercooled magma.
Scoria is another name for a highly-vesicular (almost "frothy") basalt. The black, ovals features in this photomicrograph are vesicles. Note the acicular, white plagioclase laths throughout and the euhedral, white olivine phenocryst at the lower right.
After hydrothermal alteration of vesicles in scoria: The oval feature in this photomicrograph is an amygdule: a formerly open vesicle which has been filled with a secondary mineral(s) precipitated from low-T ground waters which have penetrated into the rock. In this case, the amygdule is probably filled with a zeolite mineral.
Spherulites are radiating masses of fibrous crystals in a glassy matrix. These spherulites are probably composed of alkali feldspars and some polymorph of SiO2, and in this cross-polarized shot, appear as round objects with dark crosses. Note the large phenocryst which forms the nucleus of one of the spherulites at center-left.
A vitrophyre is another name for a phenocryst- bearing obsidian. The phenocrysts in the above photomicrograph are mostly plagioclase. The groundmass is obsidian glass.
PeliticMetamorphosed shale: slate, phyllite, mica schist, hornfels MaficMetamorphosed mafic rocks and their sediments Carbonate and calc-silicateMetamorphosed limestone, dolostone and calcareous sediments Metagraywacke (High P/LowT)Zeolite and blueschist facies rocks Granitic gneissMetamorphosed arkosic sediments, granite, rhyolite, etc.)
Typical textures of regional metamorphism: Types of foliations a. Compositional layering b. Preferred orientation of platy minerals c. Shape of deformed grains d. Grain size variation e. Preferred orientation of platy minerals in a matrix without preferred orientation f. Preferred orientation of lenticular mineral aggregates g. Preferred orientation of fractures h. Combinations of the above Figure 23.21. Types of fabric elements that may define a foliation. From Turner and Weiss (1963) and Passchier and Trouw (1996).
The crystal structure of this quartz grain has been deformed (probably by low-grade metamorphism) to produce sub-grains.
Progressive syntectonic metamorphism of a volcanic graywacke, New Zealand. From Best (1982). Igneous and Metamorphic Petrology. W. H. Freeman. San Francisco. Foliation develops due mostly to shear
Progressive syntectonic metamorphism of a volcanic graywacke, New Zealand. From Best (1982). Igneous and Metamorphic Petrology. W. H. Freeman. San Francisco. Fine-grained schist
Progressive syntectonic metamorphism of a volcanic graywacke, New Zealand. From Best (1982). Igneous and Metamorphic Petrology. W. H. Freeman. San Francisco. Well developed schist with coarser grains
Figure 23.24a. Symmetrical crenulation cleavages in amphibole-quartz-rich schist. Note concentration of quartz in hinge areas. From Borradaile et al. (1982) Atlas of Deformational and Metamorphic Rock Fabrics. Springer-Verlag.
Syn-kinematic crystals Figure 23.38. “Snowball garnet” with highly rotated spiral S i. Porphyroblast is ~ 5 mm in diameter. From Yardley et al. (1990) Atlas of Metamorphic Rocks and their Textures. Longmans.
Photomicrograph of multiple reaction rims between olivine (green, left) and plagioclase (right).
The feldspars in this alaskite from the Boulder Batholith have been largely replaced by fine-grained white mica (sericite).
Weak alteration of the plagioclase feldspar known as saussuritization is seen in this photomicrograph, the grain is also rimmed by fine grained iron- oxyhydroxide precipitating from solution.
Irregular linear alteration of olivine (O) to serpentine (S). Several steps can be recognized PPL.
Photo 6.46 - Same as 6.45. Notice that fragments belonging to the same original olivine crystal have identical interference colors, showing their � optical continuity �. XPL. Photo 6.46 - Same as 6.45. Notice that fragments belonging to the same original olivine crystal have identical interference colors, showing their � optical continuity �. XPL