This sample consists of two distinct populations distinguished by size and composition. The groundmass of elongate subhedral crystals of plagioclase, orthopyroxene and opaques is interspersed with vesicles infilled with calcite. The calcite amygdules are rimmed with quartz and occasionally chlorite.
The bulk of this sample is composed of microcrystalline limestone interspersed with calcite rhombs and transected by veinlets of clay and coarse-grained calcite.
Randomly oriented biotite phenocrysts dominate this thin section. The interstices between phenocrysts contain prisms of k-feldspar, anhedral masses of calcite and nephaline, and radial splays of muscovite. Opaques are equant and up to 0.5mm in diameter. The nephaline phase has a bluish cast in cross-polarized light. The groundmass phases are cross-cut by a mesh-work of clays and various alteration products. Slightly diamond-shaped rutile is pervasive throughout.
The groundmass of this thin section is predominantly glass with a roughly-aligned mesh-work of plagioclase, much of which has been replaced by calcite. Pseudomorphism of euhedral plagioclase phenocrysts by calcite and serpentine is pervasive; calcite grains of variable crystallographic orientations preserve the Carlsbad and albite twins characteristic of plagioclase. Throughout the sample, ellipsoids of chalcedony-rimmed serpentine masses are common; the smallest and most spherical of these have only chalcedony. The largest, amoeboid vugs of this basalt are mantled first by a rim of chalcedony, and inwards of that, a rim of serpentine. The core of the vugs contain radiating masses of an unidentified zeolite.
The crystals in this thin section look somewhat out of equilibrium with the melt. The groundmass is microcrystalline and riddled with plagioclase and pyroxenes, as well as glass. Crystals of the phenocryst population are generally subhedral, with rounded corners and irregular twins. The pyroxenes are frequently rimmed by pyroxenes of differing composition. Plagioclase phenocrysts are of differing generations; the first has cloudy, inclusion-rich cores with fresh rims and the second lacks this core. Both may be concentrically zoned. The pyroxenes in particular tend to cluster in glomeroporphyroclasts. The occasional granular aggregate of calcite can be observed in this sample.
The least altered phase in this thin section is plagioclase, which forms roughly aligned, variably sized laths that make up both the groundmass, which is dominantly glass, and the phenocryst population. A second phenocryst, clinopyroxene, remains only as inclusions in the calcite pseudomorphs that replaced it. Vesicles, clays, and hematite pseudomorphs are abundant in this thin section.
Large, interlocking calcite crystals comprise this marble. This thin section is useful for finding interference figures.
Large, euhedral to subhedral plagioclase blocks are in far greater abundance than either k-feldspar or quartz, both of which are anhedral in shape. All the ferromagnesian phases are anhedral in shape and tend to cluster together. Hornblende growth is at the expense of clinopyroxene. Opaques cluster with the ferromagnesian phases. Quartz displays first-order yellows in this slightly thickened sample.
A groundmass of glass, clay, calcite, indiscernible quartzofeldspathic crystals, and small, spherical aggregates of chalcedony dominate this sample. Phenocrysts of biotite and calcite pseudomorphs after plagioclase (presumably) comprise the phaneritic crystal population.
This coarse-grained dacite has a granitic texture of hypidiomorphic inequigranular plagioclase, hornblende, and augite. Secondary zeolites and calcite are found randomly throughout. This thin section is both too thick and plucking is disruptive of many hornblende grains.
A few biotite phenocrysts punctuation this sample's fine-grained groundmass of unoriented elongate biotite, k-feldspar, nephaline crystals and anhedral calcite masses.
This fine-grained, hypidiomorphic, inequigranular plutonic rock is intermediate in composition, with plagioclase as the dominant feldspar. K-feldspar is present in much lower abundance, and quartz is scarce. Mafic phases include anhedral biotite and hornblende, the latter of which is strongly chloritized.
The grain size of plagioclase laths in this porphyritic basalt ranges continuously from the groundmass microlites to milimetric phenocrysts. Glass and sparse equant pyroxenes comprise the remainder of the groundmass. Clinopyroxene phenocrysts are patchy due to plucking.
The plagioclase laths in this microporphyritic basalt are separated by size into seperate groundmass and phenocryst populations. Glass and opaques are the other groundmass phases. Clinopyroxene and its periodic pseudomorph calcite are additional phenocrysts.
The elongate minerals, glaucophane, clinozoisite and muscovite define the foliation in this sample, which is tightly folded in a crenulation cleavage.
Moderately sorted, subangular, matrix-supported, quartz and glauconite sandstone with calcite and hematite matrix. Quartz is undulatory with subgrain walls developing and potassium feldspar twins are deformed. Pockets of finer-grained material contain rounded epidote grains.
A very poorly sorted rock with variably sized and angular quartz and feldspar pieces (both plagioclase and orthoclase; some fresh, others sericitized) set in a finer-grained matrix of chlorite, sericite, carbonate, silky quartz, leucoxene, magnetite and pyrite. Matrix chlorite corrodes quartz grains marginally. A few microfragments of rock (quartzite, granite, gneiss) also are present. Accessory detritals include muscovite, sphene, tourmaline and epidote. Most of the quartz pieces are markedly undulatory. A very low degree of incipient metamorphism is indicated by abundant secondary epidote in the matrix which also locally contains minute platelets of stilpnomelane.
Poorly-sorted, angular, clast-supported, arkosic conglomerate with large clasts of deformed quartz and microcline. Many feldspar grains are altering to clays. Deformed micas are interspersed throughout. Perthite and scotch-plaid twins are extensive. The cement is comprised of microcrystalline quartz and locally, calcite.
This porous, fine-grained, well-sorted, well-rounded, clast-supported quartz sandstone is cemented together with hematite. Clasts of microcline, hornblende, calcite, and chert are dispersed in minor amounts throughout the sample. The layering which is visible to the naked eye is unnoticeable in thin section.
The bulk of this sample is composed of microcrystalline limestone interspersed with calcite rhombs and transected by veinlets of clay and coarse-grained calcite. According to the collectors, this sample was collected because of its replacement textures.
A moderately-sorted, subrounded quartz sandstone with a calcite cement. Microcline and albite are present in smaller amounts than the quartz clasts. A luster-mottling texture is present, in which the calcite cement forms crystals larger than the clasts it cements, as indicated by the optical continuity and parallel twins across large portions of the thin section's cement. Layering is observed in thin section by zones of abundant cement alternating with more clast-supported, calcite-poor zones. Most quartz clasts show undulatory extinction and subgrain development.
This porphyritic sample contains phenocrysts of augite, olivine, and pseudoleucite. Olivine has an iddingsite rim when in contact with the groundmass. The pseudoleucite phenocrysts are a colorless and cloudy, roundish eight-sided crystals with first-order grey birefringence and extinction occurs in amoeboid-shaped sections within the phenocryst. These same pseudoleucite crystals make up the majority of the groundmass, along with calcite, k-feldspar and other alteration products. Three copies of this thin section contain the contact zone itself, with a calcite and clay-rich, layered Eagle sandstone.
This hypocrystalline thin section contains a trachytic groundmass of plagioclase laths, biotite needles, elongate strings of quartz, and serpentine pseudomorphs. The phenocrystic population consists of rounded quartz grains, often with a calcite rim, and concentrically-zoned, euhedral to subhedral plagioclase blocks. The plagioclase is being replaced in places by calcite, which is also found in fractures within the sample.
The micas in this hypocrystalline rhyolite form euhedral needles and are generally aligned. Phenocrysts of plagioclase have been replaced by calcite and chalcedony. The groundmass of glass contains indiscernible crystals. This thin section is strongly altered and due to the fine grain size, difficult to identify minerals in.
The four phenocrystic phases in this thin section all display disequilibrium textures. Tabular plagioclase pheoncrysts are oscillatorily-zoned at the core and surrounded by as many as three distinct, cloudy, inclusion-rich rims. Quartz phenocrysts are rounded by resorbtion; thick coronas of calcite and hematite pepper, though do not entirely replace, their rims. Relict biotite phenocrysts, pseudomorphed by an opaque phase, are recognized more readily by the consistant rectancular and hexagonal shape than by the rare inclusion of the residual 'host'. These grains, frequently clustered together, have thick black rims and are sometimes infilled with a calcite-like mineral. This calcite-like mineral, frequently found replacing the biotite and as part of the quartz phenocryst coronas, is also observed pseudomorphing a tabular-shaped mineral found both as a phenocryst and part of the groundmass. The calcite seems to be replacing rectangular serpentine phenocrysts, presumably, pyroxene pseudomorphs themselves. The trachytic groundmass consists predominantly of microlites of plagioclase, prismatic opaques, glass, and the periodic rectangular calcite pseudomorph. Granular hematite veins cross-cut the thin section.