Where is variolite found?
Where is variolite found?
Variolitic pillow lavas, that have been previously identified as variolites and also classified as spilites, are found in the Durance, France; on Mont Genvre, France; in Devonian rocks of Germany; and as cobbles on the beaches of the Strait of Juan de Fuca along the northern edge of the Olympic Peninsula.
What is variole?
noun. a shallow pit or depression like the mark left by a smallpox pustule; foveola. a light-colored spherule, common in some igneous rocks, that gives a pockmarked appearance to weathered rock surfaces.
How are Variolites formed?
Microscopy reveals that varioles result either from blotchy alteration or magma mingling, or they are a form of plagioclase spherulite. Their internal organization and geochemistry is incompatible with the concept that they are quenched immiscible liquids, as has been suggested by some authors (Gélinas et al., 1977).
What is Variolitic texture?
variolitic Applied to a spherulitic texture consisting of fine, radiating fibres of plagioclase or pyroxene that is found in the glassy, chilled margin of shallow-level, basic, igneous intrusions (dykes and sills) or the glassy groundmass of some quenched (see QUENCHING) basaltic lavas.
How are spherulites formed?
Spherulites frequently have a radiating structure that results from an intergrowth of quartz and orthoclase. These spherical bodies are thought to have formed as a consequence of rapid mineral growth after nucleation, possibly on an accumulation of volatiles.
Why are Komatiites rare on Earth’s surface today?
Komatiite is an exceedingly rare type of lava. No volcano on Earth erupts this material today. Komatiites are essentially restricted to the Archean (4.55 to 2.5 billion years ago), when Earth’s heat flux was much higher.
What is cumulate texture?
Cumulate rocks are named according to their texture; cumulate texture is diagnostic of the conditions of formation of this group of igneous rocks. Cumulates can be deposited on top of other older cumulates of different composition and colour, typically giving the cumulate rock a layered or banded appearance.
What is Spherulitic texture?
Spherulites and spherulitic textures are a. common product of devitrification of terrestrial. rhyolite glasses [Lofgren, 1970, 1971]. Many. of the glass fragments in the lunar breccias.
What do you mean by spherulites?
Definition of spherulite : a usually spherical crystalline body of radiating crystal fibers often found in vitreous volcanic rocks.
What are lamellae and spherulites?
Spherulites are composed of highly ordered lamellae, which result in higher density, hardness, but also brittleness when compared to disordered regions in a polymer. The lamellae are connected by amorphous regions which provide elasticity and impact resistance.
Why are komatiites important?
Komatiite-hosted nickel-copper sulfide mineralisation today accounts for about 14% of the world’s nickel production, mostly from Australia, Canada and South Africa. Komatiites are associated with nickel and gold deposits in Australia, Canada, South Africa and most recently in the Guiana shield of South America.
What is Trachytic texture?
Trachytic is a texture of extrusive rocks in which the groundmass contains little volcanic glass and consists predominantly of minute tabular crystals, namely, sanidine microlites. The microlites are parallel, forming flow lines along the directions of lava flow and around inclusions.
What is the origin of the term variolite?
In 1648, Aldrovandi created the term variolite for aphanitic or fine-grained igneous rocks containing varioles. The weathering of varioles often cause variolites to have a pock-marked appearance. In allusion to the pock-marked appearance of weathered surfaces of variolite, this term is derived from the Latin word, variola, for smallpox.
What are varioles in rocks?
Varioles are millimeter- to centimeter-scale, light-colored, globular to spherical structures, that are conspicuously observable within aphanitic, mafic igneous rocks, such as basalt, komatiite, and tachylite, that comprise either pillow lavas, subaerial lava flows, or volcanic dykes.
What are the different varieties of variolites?
The major varieties of variolites are variolitic basalts, variolitic pillow lavas and variolitic komatiites.