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Basalt (UK: / ˈ b æ s ɒ l t,-ɔː l t,-əl t /; [1] [2] US: / b ə ˈ s ɔː l t, ˈ b eɪ s ɔː l t /) [3] is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon.
The individual crystals in an aphanitic igneous rock are not distinguishable to the naked eye. Examples of aphanitic igneous rock include basalt, andesite, and rhyolite. Glassy or vitreous textures occur during some volcanic eruptions when the lava is quenched so rapidly that crystallization cannot occur. The result is a natural amorphous glass ...
Beach pebble of variolitic pillow lava (varolite) from the Olympic Peninsula, Washington stateVariolites are mafic, igneous, and typically volcanic rocks, e.g. tholeiite, basalt or komatiite, that contain centimeter-scale spherical or globular structures, called varioles, in a fine-grained matrix.
Granite, basalt and some metamorphic stone is difficult to carve even with iron or steel tools; usually tungsten carbide tipped tools are used, although abrasives still work well. Modern techniques often use abrasives attached to machine tools to cut the stone.
The smooth texture of this basaltic volcanic bomb is aphanitic. IUGS classification of aphanitic extrusive igneous rocks according to their relative alkali (Na 2 O + K 2 O) and silica (SiO 2) weight contents. Blue area is roughly where alkaline rocks plot; yellow area where subalkaline rocks plot. [1]
Scoria differs from pumice, another vesicular volcanic rock, in having larger vesicles and thicker vesicle walls, and hence is denser.The difference is probably the result of lower magma viscosity, allowing rapid volatile diffusion, bubble growth, coalescence, and bursting.
The basal contact of the Cardenas Basalt with the underlying Dox Formation is smooth, planar, parallel to bedding and locally interfingering. In places the sandstones of the Dox Formation have small folds and convolutions that are indicative of soft sediment deformation. In addition, in places, the uppermost 60 cm (2.0 ft) of the Dox Formation ...
Sideromelane is partially transparent because it contains much fewer crystals. Sideromelane is abundant only in eruptions where basalt magma has been very rapidly cooled by contact with water, such as phreatomagmatic eruptions. [5] Basaltic volcanic glass is also present in pillow lavas. [6]