Intergrown, subhedral two-pyroxene gabbro with hornblende and poikilitic plagiclase with deformation twins and abundant pyroxene inclusions.
This medium-grained allotriomorphic diorite is dominated by plagioclase, much of which is concentrically zoned and larger in size than most other phases in the sample. Clusters of the ferromagnesian phases appear to be pseudomorphing a previous, rectangular, phenocrystic phase.
The phenocrysts in this porphyritic granite are inclusion-rich, clay-altered, subhedral plagioclase blocks that do not appear to be in equilibrium with the surrounding groundmass. The groundmass is a mottled smattering of quartzofeldspathic minerals that have no discernable crystal habit. Amidst the background blur of first-order whites and grays are petrographically messy clusters of chlorite, hornblende, and iddingsite, with growth of chlorite and iddingsite at the expense of hornblende. Large, prismatic and hexagonal apatite crystals are readily apparent in this thin section. A few prismatic crystals of monazite, zircon, or xenotime are present (though difficult to definitively identify).
The subhedral hornblende crystals in the sample align with the micas to form a spaced foliation separating microlithons of plagioclase and quartz. Equant subhedral epidote crystals punctuate the rock. Biotite and chlorite are typically interfingered and chlorite display anomalous blue interference colors. Elongate granular aggregates of light brown to colorless titanite are present.
Phenocrystic phases in this thin section are subhedral plagioclase, clinopyroxene, and orthopyroxene, found both as isolated crystals and as glomeroporphyroclasts. Some plagioclase phenocrysts have inclusions of equant pyroxenes and blebs of glass. Glass and plagioclase comprise the vesicular groundmass.
This cryptocrystalline basalt consists of a groundmass of plagioclase microlites, equant opaques, glass, and interstitial, anhedral phlogopite. Microphenocrysts of subhedral clinopyroxene comprise the remainder of the sample.
Based on grain size, two populations of pyroxenes and plagioclase exist in this sample; the first are the fine-grained, equant crystals of the glassy groundmass, and the second, the subhedral to anhedral phenocrysts visible in handsample. The inconsistently-shaped plagioclase grains are sometimes zoned and frequently contain inclusions of glass.
Square phenocrysts of quartz and feldspar disrupt this porphyritic granite's otherwise mosaic of equigranular grains. Subhedral and partially resorbed biotite is scattered throughout.
This thin section is comprised entirely of glass and aligned plagioclase microlites. A few hematite nodules are found throughout. One weathered biotite phenocrysts can be seen.
The groundmass of this porphyritic basalt is predominantly glass with less abundant plagioclase microlites. The most readily-identifiable mineral of the phenocryst population is plagioclase. Of greater abundance are euhedral, opaque pseudomorphs. Rare inclusions of pyroxene are observed within these opaques. Pockets of chalcedony disrupt the otherwise uniform groundmass.
Allotriomorphic plagioclase and highly-fractured olivine are the dominant minerals in this thin section. Clinopyroxene, when present, is found adjacent to olivine. Fractured zones in this rock follow olivine clusters and frequently cross-cut plagioclase crystals in swarms between nodes of granular olivine.
Unoriented plagioclase laths and interstitial glass and clinopyroxene make up the groundmass of this vesicular basalt. Olivine and orthopyroxene microphenocrysts are scattered throughout.
The olivine that is so conspicuous in the JPN-3 handsample is conspicuously absent in thin section and represented by a mere 1 or 2 grains. Rather, phenocrysts of plagioclase and pyroxenes dominate the phaneritic phases. Both phases are subhedral and the plagioclase in particular indicates several different generations of growth. Some plagioclase is concentrically zoned, though most grains contain alternating inclusion-rich and poor zones. Inclusions are of pyroxenes and glass blebs. The groundmass contains glass, plagioclase microlites, and tiny pyroxenes.
Although labeled an andesite on the sample record sheet, the presence of olivine and absence of hydrous mafic phases in this thin section indicate it is more basaltic in composition. Texturally, it is characteristic of a basalt as well, with a glassy and plagioclase-rich groundmass and phenocrysts of plagioclase, both pyroxenes and olivine. All phenocrysts are subhedral and plagioclase contains inclusions of glass.
Unaligned, prismatic crystals of schorl, with strongly mauve to indigo pleochroism and concentric compositional zoning are scattered throughout the sample. Basal sections remain a deep blue regardless of rotation of the stage. A corona of clear tourmaline (perhaps) rims most grains. The tourmaline are found in a sericitized feldspars.
This sample has a granoblastic texture defined by feldspars, garnet, and pyroxene. Crystals of all phases are roughly equant in shape. Alteration is concentrated along the rare hornblende grains and more commonly throughout the pyroxenes. Calcite and apatite are accessory phases and chlorite is found as an alteration product.
Grain boundaries between the quartz and feldspar phases in this sample are consistently lobate, often with finer-grained subgrains rimming each crystal. Quartz in undulatory. The mica phases are subhedral and often resorbed, with kink bands causing undulose extinction along the length of the grain. Along one edge of the thin section is a seam dominated by clinozoisite. A hematite stain gives a dusty orange appearance to the feldspars and fractures within the sample contain higher concentrations of the phase.
This hypidiomorphic inequigranular granite has rather scalloped grain boundaries, particularly among the quartzofeldspathic phases, though the biotite grains exhibit similar textures with the feldspars. One anhedral biotite grain has bulbs protruding into the neighboring k-feldspar grain. Quartz extinction is uniform. Olivine is present in trace amounts and the highly-fractured phase is typically surrounded by a thick rim of iddingsite.
Phenocrysts of resorbed plagioclase and k-feldspar give this otherwise glassy rock its porphyritic texture. A couple of resorbed pyroxene phenocrysts are present. Aligned needles of an opaque phase give the glassy groundmass a trachytic texture.
The olivine phenocrysts in this vesicular basalt are unaltered, in contrast to the second phenocrystic phase, plagioclase, which has a speckled, mottled alteration texture encroaching concentrically inwards from the grain boundaries. Only the cores and a thin corona of plagioclase on the outermost edges of the phenocrysts remains unaltered by this opaque phase. The glassy groundmass contains of unoriented plagioclase microlites and tiny olivine crystals. Olivine phenocrysts are smaller and less abundant in CF1B than CF1A. Plucking of olivine crystals is extensive.
The plagioclase lath in this aphanitic basalt are generally all the same size and are strongly aligned to form a classic trachytic texture with interstitial olivine. A few larger crystals of both phases are observed.
Like KRB10, plagioclase and clinopyroxene are intergrown in an almost graphic texture, though where KRB10 was dominated by the unknown mineral, in KRB11, that unknown mineral is confined to spherulite-like clusters in a fine-grained quartz matrix. Iddingsite alteration is much less extensive. Western Minerals Inc. as an 'interstitial ferrotholeiite, very highly fractionatedâ€¦textures are similar to those associated with rapidly frozen or highly viscous melts.'
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 groundmass of glass and plagioclase microlites is host to euhedral phenocrysts of three euhedral mineral phases, plagioclase, hornblende, and biotite.
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.