Blairmorite

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Blairmorite
Extrusive igneous rock
Blairmorite from the Crowsnest Formation.jpg
A specimen of blairmorite from the Crowsnest Formation. The amber mineral is analcime, the pale mineral is sanidine and the small black minerals are melanite garnet.
Composition
Primary Analcime, sanidine, pyroxene
Secondary Titanite, melanite, nepheline

Blairmorite is a very rare [1] porphyritic volcanic rock named after the community of Blairmore in southwestern Alberta, Canada. [2] [3] It is characterized by dominant analcime phenocrysts in a matrix of analcime, sanidine and alkalic pyroxene with accessory titanite, melanite and nepheline. It is a leucocratic variety of analcimite (a foidite). [4] Blairmorite has also been described as an analcime-rich variety of phonolite. [5] [6]

This extrusive igneous rock is known from only two geological formations worldwide. The foremost blairmorite occurrence is the Crowsnest Formation in the Canadian province of Alberta where it is associated with agglomerates and tuffs from explosive eruptions. The other locality is the Lupata Gorge in Mozambique. [2]

Related Research Articles

<span class="mw-page-title-main">Analcime</span> Tectosilicate mineral

Analcime (; from Ancient Greek ἀνάλκιμος (análkimos) 'not strong') or analcite is a white, gray, or colorless tectosilicate mineral. Analcime consists of hydrated sodium aluminium silicate in cubic crystalline form. Its chemical formula is NaAlSi2O6·H2O. Minor amounts of potassium and calcium substitute for sodium. A silver-bearing synthetic variety also exists (Ag-analcite). Analcime is usually classified as a zeolite mineral, but structurally and chemically it is more similar to the feldspathoids. Analcime isn't classified as an isometric crystal, as although the crystal structure appears to be isometric, it is usually off only by a fraction of an angle. However, there are truly isometric samples of the mineral, which makes its classification even more difficult. Due to the differences between the samples being too slight, there's no merit from having multiple species names, so as a result analcime is a common example for minerals occurring in multiple crystal systems and space groups. It was first described by French geologist Déodat de Dolomieu, who called it zéolithe dure, meaning hard zeolite. It was found in lava in Cyclops, Italy. The mineral is IMA approved, and had been grandfathered, meaning the name analcime is believed to refer to a valid species til this day.

<span class="mw-page-title-main">Rhyolite</span> Igneous, volcanic rock, of felsic (silica-rich) composition

Rhyolite is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent to granite.

<span class="mw-page-title-main">Phonolite</span> Uncommon extrusive rock

Phonolite is an uncommon shallow intrusive or extrusive rock, of intermediate chemical composition between felsic and mafic, with texture ranging from aphanitic (fine-grained) to porphyritic (mixed fine- and coarse-grained). Phonolite is a variation of the igneous rock trachyte that contains nepheline or leucite rather than quartz. It has an unusually high (12% or more) Na2O + K2O content, defining its position in the TAS classification of igneous rocks. Its coarse grained (phaneritic) intrusive equivalent is nepheline syenite. Phonolite is typically fine grained and compact. The name phonolite comes from the Ancient Greek meaning "sounding stone" due to the metallic sound it produces if an unfractured plate is hit; hence, the English name clinkstone is given as a synonym.

<span class="mw-page-title-main">Porphyry (geology)</span> Textural form of igneous rock with large grained crystals in a fine matrix

Porphyry is any of various decorative granites or igneous rocks with coarse-grained crystals such as feldspar or quartz dispersed in a fine-grained silicate-rich, generally aphanitic matrix or groundmass. The larger crystals are called phenocrysts. In its non-geologic, traditional use, the term porphyry usually refers to the purple-red form of this stone, valued for its appearance, but other colours of decorative porphyry are also used such as "green", "black" and "grey".

<span class="mw-page-title-main">Porphyritic</span> Igneous rock with large and small crystals

Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning all types of igneous rocks can display some degree of porphyritic texture. Most porphyritic rocks have bimodal size ranges, meaning the rock is composed of two distinct sizes of crystal.

<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">Scoria</span> Dark vesicular volcanic rock

Scoria is a pyroclastic, highly vesicular, dark-colored volcanic rock formed by ejection from a volcano as a molten blob and cooled in the air to form discrete grains called clasts. It is typically dark in color, and basaltic or andesitic in composition. Scoria has relatively low density, as it is riddled with macroscopic ellipsoidal vesicles, but in contrast to pumice, scoria always has a specific gravity greater than 1 and sinks in water.

<span class="mw-page-title-main">Phenocryst</span> Crystal larger than the rock grains that surround it in an igneous rock

A phenocryst is an early forming, relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of an igneous rock. Such rocks that have a distinct difference in the size of the crystals are called porphyries, and the adjective porphyritic is used to describe them. Phenocrysts often have euhedral forms, either due to early growth within a magma, or by post-emplacement recrystallization. Normally the term phenocryst is not used unless the crystals are directly observable, which is sometimes stated as greater than .5 millimeter in diameter. Phenocrysts below this level, but still larger than the groundmass crystals, are termed microphenocrysts. Very large phenocrysts are termed megaphenocrysts. Some rocks contain both microphenocrysts and megaphenocrysts. In metamorphic rocks, crystals similar to phenocrysts are called porphyroblasts.

<span class="mw-page-title-main">Lamprophyre</span> Ultrapotassic igneous rocks

Lamprophyres are uncommon, small-volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks, and small intrusions. They are alkaline silica-undersaturated mafic or ultramafic rocks with high magnesium oxide, >3% potassium oxide, high sodium oxide, and high nickel and chromium.

<span class="mw-page-title-main">Rhyodacite</span> Volcanic rock rich in silica and low in alkali metal oxides

Rhyodacite is a volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of those plutonic rocks that are intermediate in composition between monzogranite and granodiorite. Rhyodacites form from rapid cooling of lava relatively rich in silica and low in alkali metal oxides.

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

Sanidine is the high temperature form of potassium feldspar with a general formula K(AlSi3O8). Sanidine is found most typically in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal system. Orthoclase is a monoclinic polymorph stable at lower temperatures. At yet lower temperatures, microcline, a triclinic polymorph of potassium feldspar, is stable.

<span class="mw-page-title-main">Crowsnest Mountain</span> Mountain in Alberta, Canada

Crowsnest Mountain is a mountain in the southern Canadian Rockies of southwestern Alberta, Canada. It can be seen from Alberta Highway 3 west of the town of Coleman in the Crowsnest Pass. The mountain was originally named by the Ktunaxa First Nations due to ravens nesting in the area. The scrambling route on the north side was first ascended in 1915.

<span class="mw-page-title-main">Blairmore, Alberta</span> Former village in Alberta, Canada

Blairmore is a community in the Rocky Mountains within the Municipality of Crowsnest Pass in southwest Alberta, Canada. It was formerly incorporated as a town prior to 1979 when it amalgamated with four other municipalities to form Crowsnest Pass. Blairmore is the principal commercial centre of Crowsnest Pass.

Type locality, also called type area, is the locality where a particular rock type, stratigraphic unit or mineral species is first identified. If the stratigraphic unit in a locality is layered, it is called a stratotype, whereas the standard of reference for unlayered rocks is the type locality.

<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.

<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">Shoshonite</span> Potassium-rich variety of basaltic trachyandesite

Shoshonite is a type of igneous rock. More specifically, it is a potassium-rich variety of basaltic trachyandesite, composed of olivine, augite and plagioclase phenocrysts in a groundmass with calcic plagioclase and sanidine and some dark-colored volcanic glass. Shoshonite gives its name to the shoshonite series and grades into absarokite with the loss of plagioclase phenocrysts and into banakite with an increase in sanidine. Shoshonite was named by Iddings in 1895 for the Shoshone River in Wyoming. Textural and mineralogical features of potash-rich rocks of the absarokite-shoshonite-banakite series strongly suggest that most of the large crystals and aggregates are not true phenocrysts as previously thought but are xenocrysts and microxenoliths, suggesting a hybrid origin involving assimilation of gabbro by high-temperature syenitic magma.

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

The Palliser Formation is a stratigraphic unit of Late Devonian (Famennian) age in the Western Canada Sedimentary Basin. It is a thick sequence of limestone and dolomitic limestone that is present in the Canadian Rockies and foothills of western Alberta. Tall cliffs formed of the Palliser Formation can be seen throughout Banff and Jasper National Parks.

<span class="mw-page-title-main">Kenyte</span> Type of igneous rock

Kenyte is a type of igneous rock. More specifically, it is a variety of porphyritic phonolite or trachyte with rhomb-shaped phenocrysts of anorthoclase with variable amounts of olivine and augite in a glassy matrix; the glass may be devitrified.

References

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  1. MacKenzie, W.S., Donaldson, C.H. and Guilford, C. (1982). Atlas of igneous rocks and their textures. Harlow: Longman. p. 121. ISBN   0-582-30082-7.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. 1 2 Pearce, T.H. (1993). "Analcime phenocrysts in igneous rocks: Primary or secondary? – Discussion" (PDF). American Mineralogist. 78: 225–229.
  3. Johannsen, A. 1933. A descriptive petrography of the igneous rocks, Appendix III, p. 244. Univ. of Chicago Press.
  4. Le Maitre, R.W. (editor) (2002). Igneous Rocks — A Classification and Glossary of Terms (2nd ed.). Cambridge: Cambridge University Press. pp. 55, 64. ISBN   0-521-66215-X.{{cite book}}: |author= has generic name (help)
  5. Peterson, T.D.; Currie, K.L. (1993). Analcite-bearing igneous rocks from the Crowsnest Formation, southwestern Alberta (Current Research report 93-B1) (PDF). Geological Survey of Canada. pp. 51–56.
  6. Deer, W.A.; Howie, R.A.; Zussman, J. (2013). An Introduction to the Rock-Forming Minerals (3rd ed.). London: Mineralogical Society. ISBN   9780903056274.