Hyalopilitic

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Hyalopilitic is a textural term used in petrographic classification of volcanic rocks. Specifically, hyalopilitic refers to a volcanic rock groundmass, which is visible only under magnification with a petrographic microscope, that contains a mixture of very fine-grained mineral crystals either mixed with natural volcanic glass, or surrounded by thin bands of volcanic glass.

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<span class="mw-page-title-main">Pumice</span> Light colored highly vesicular volcanic rock

Pumice, called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular volcanic rock that differs from pumice in having larger vesicles, thicker vesicle walls, and being dark colored and denser.

<span class="mw-page-title-main">Extrusive rock</span> Mode of igneous volcanic rock formation

Extrusive rock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff. In contrast, intrusive rock refers to rocks formed by magma which cools below the surface.

<span class="mw-page-title-main">Volcanic rock</span> Rock formed from lava erupted from a volcano

Volcanic rock is a rock formed from lava erupted from a volcano. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and metamorphic rocks and constitute an important element of some sediments and sedimentary rocks. For these reasons, in geology, volcanics and shallow hypabyssal rocks are not always treated as distinct. In the context of Precambrian shield geology, the term "volcanic" is often applied to what are strictly metavolcanic rocks. Volcanic rocks and sediment that form from magma erupted into the air are called "pyroclastics," and these are also technically sedimentary rocks.

<span class="mw-page-title-main">Felsite</span> Very fine-grained volcanic rock that sometimes contains larger crystals

Felsite is a very fine-grained volcanic rock that may or may not contain larger crystals. Felsite is a field term for a light-colored rock that typically requires petrographic examination or chemical analysis for more precise definition. Color is generally white through light gray, or red to tan and may include any color except dark gray, green or black. The mass of the rock consists of a fine-grained matrix of felsic materials, particularly quartz, sodium and potassium feldspar, and may be termed a quartz felsite or quartz porphyry if the quartz phenocrysts are present. This rock is typically of extrusive origin, formed by compaction of fine volcanic ash, and may be found in association with obsidian and rhyolite. In some cases, it is sufficiently fine-grained for use in making stone tools. Its fine texture and felsic components allow for good knapped pieces, much like working chert, producing conchoidal fracture.

<span class="mw-page-title-main">Scoria</span> Dark vesicular volcanic rock

Scoria is a pyroclastic, highly vesicular, dark-colored volcanic rock that was ejected from a volcano as a molten blob and cooled in the air to form discrete grains or clasts. It is typically dark in color, and basaltic or andesitic in composition. Scoria is relatively low in density as a result of its numerous macroscopic ellipsoidal vesicles, but in contrast to pumice, all scoria has a specific gravity greater than 1 and sinks in water.

Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. The classification of rocks is based on the information acquired during the petrographic analysis. Petrographic descriptions start with the field notes at the outcrop and include macroscopic description of hand specimens. The most important petrographer's tool is the petrographic microscope. The detailed analysis of minerals by optical mineralogy in thin section and the micro-texture and structure are critical to understanding the origin of the rock.

<span class="mw-page-title-main">Apache tears</span> Popular term for pebbles of obsidian

Apache tears are rounded pebbles of obsidian or "obsidianites" composed of black or dark-colored natural volcanic glass, usually of rhyolitic composition and bearing conchoidal fracture. Also known by the lithologic term marekanite, this variety of obsidian occurs as subrounded to subangular bodies up to about 2 in (51 mm) in diameter, often bearing indented surfaces. Internally the pebbles sometimes contain fine bands or microlites and though in reflected light they appear black and opaque, they may be translucent in transmitted light. Apache tears fall between 5 and 5.5 in hardness on the Mohs scale.

<span class="mw-page-title-main">Komatiite</span> Ultramafic mantle-derived volcanic rock

Komatiite is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava of at least 18 wt% magnesium oxide (MgO). It is classified as a 'picritic rock'. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiite was named for its type locality along the Komati River in South Africa, and frequently displays spinifex texture composed of large dendritic plates of olivine and pyroxene.

<span class="mw-page-title-main">Pyroxferroite</span>

Pyroxferroite (Fe2+,Ca)SiO3 is a single chain inosilicate. It is mostly composed of iron, silicon and oxygen, with smaller fractions of calcium and several other metals. Together with armalcolite and tranquillityite, it is one of the three minerals which were discovered on the Moon during the 1969 Apollo 11 mission. It was then found in Lunar and Martian meteorites as well as a mineral in the Earth's crust. Pyroxferroite can also be produced by annealing synthetic clinopyroxene at high pressures and temperatures. The mineral is metastable and gradually decomposes at ambient conditions, but this process can take billions of years.

<span class="mw-page-title-main">Fiamme</span> Small lens-shaped inclusions in volcaniclastic rocks

Fiamme are lens-shapes, usually millimetres to centimetres in size, seen on surfaces of some volcaniclastic rocks. They can occur in welded pyroclastic fall deposits and in ignimbrites, which are the deposits of pumiceous pyroclastic density currents. The name fiamme comes from the Italian word for flames, describing their shape. The term is descriptive and non-genetic.

<span class="mw-page-title-main">Pigeonite</span>

Pigeonite is a mineral in the clinopyroxene subgroup of the pyroxene group. It has a general formula of (Ca,Mg,Fe)(Mg,Fe)Si2O6. The calcium cation fraction can vary from 5% to 25%, with iron and magnesium making up the rest of the cations.

<span class="mw-page-title-main">Texture (geology)</span>

In geology, texture or rock microstructure refers to the relationship between the materials of which a rock is composed. The broadest textural classes are crystalline, fragmental, aphanitic, and glassy. The geometric aspects and relations amongst the component particles or crystals are referred to as the crystallographic texture or preferred orientation. Textures can be quantified in many ways. The most common parameter is the crystal size distribution. This creates the physical appearance or character of a rock, such as grain size, shape, arrangement, and other properties, at both the visible and microscopic scale.

In petrology, micrographic texture is a fine-grained intergrowth of quartz and alkali feldspar, interpreted as the last product of crystallization in some igneous rocks which contain high or moderately high percentages of silica. Micropegmatite is an outmoded terminology for micrographic texture.

<span class="mw-page-title-main">Igneous textures</span>

Igneous textures include the rock textures occurring in igneous rocks. Igneous textures are used by geologists in determining the mode of origin of igneous rocks and are used in rock classification. The six main types of textures are phaneritic, aphanitic, porphyritic, glassy, pyroclastic, and pegmatitic.

<span class="mw-page-title-main">Szentbékkálla</span> Place in Veszprém, Hungary

Szentbékkálla is a village in Káli-basin, Balaton-Highlands, Veszprém county, Hungary. In the Middle Ages the village had a monastery of St. Benedict, which explains its name, because earlier it was Szentbenedekkál. Kál was a prince and landlord here in the ages of the Árpád's peoples arrival to Hungary.

In igneous petrology, eutaxitic texture describes the layered or banded texture in some extrusive rock bodies. It is often caused by the compaction and flattening of glass shards and pumice fragments around undeformed crystals.

<span class="mw-page-title-main">Crowsnest Formation</span>

The Crowsnest Formation, also called the Crowsnest Volcanics, is a geological formation in southwestern Alberta, Canada, on the southwestern margin of the Western Canada Sedimentary Basin. It was named for the Crowsnest Pass near Coleman, Alberta. The formation consists mostly of pyroclastic rocks that were laid down in a series of explosive eruptions about 100 million years ago during the Albian stage of the Early Cretaceous epoch. It contains unusual minerals such as melanite and analcime.

<span class="mw-page-title-main">Glass House Mountains</span> Mountain range in Queensland, Australia

The Glass House Mountains are a cluster of thirteen hills that rise abruptly from the coastal plain on the Sunshine Coast, Queensland, Australia. The highest hill is Mount Beerwah at 556 metres above sea level, but the most identifiable of all the hills is Mount Tibrogargan which from certain angles bears a resemblance to a face staring east towards the ocean. The Glass House Mountains are located near Beerburrum State Forest and Steve Irwin Way. From Brisbane, the mountains can be reached by following the Bruce Highway north and taking the Glass House Mountains tourist drive turn-off onto Steve Irwin Way. The trip is about one hour from Brisbane. The Volcanic peaks of the Glass House Mountains rise dramatically from the surrounding Sunshine Coast landscape. They were formed by intrusive plugs, remnants of volcanic activity that occurred 26–27 million years ago. Molten rock filled small vents or intruded as bodies beneath the surface and solidified into land rocks. Millions of years of erosion have removed the surrounding exteriors of volcanic cores and softer sandstone rock.