Glossary of Rock and Mineral Terms - V

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valley glacier

An alpine glacier that flows through a preexisting stream valley.

vanadates

Group of minerals that are compounds of one or more metallic element associated with the vanadate radical (VO₄). The vanadates, together with the related arsenates, are classified in the phosphate group. Most vanadates are heavy, and none are hard. They are usually brittle and occur in small crystals or compact aggregates.

van der Waals bond

A relatively weak kind of intermolecular bond that forms when one side of a molecule develops a slight negative charge because a number of electrons have temporarily moved to that side of the molecule. This negative charge attracts the nuclei of the atoms of a neighboring molecule. The side of the molecule with fewer electrons develops a slight positive charge that attracts the electrons of the atoms of neighboring molecules.

variable formula

Chemical formula of a mineral that includes all common elemental replacements. For example, the mineral Adamite - Zn₂(AsO₄)(OH), frequently contains part of the zinc (Zn) replaced by copper (Cu) or cobalt (Co); thus its variable formula is (Zn,Cu,Co)₂(AsO₄)(OH).

variety

Titled variable of a mineral, characterized by a special property not present in other members of that same mineral such as color, location, chemical additive, crystal or aggregate, etc.

varve

A pair of sediment beds deposited by a lake on its floor, typically consisting of a thick, coarse, light-colored bed deposited in the summer and a thin, fine-grained, dark-colored bed deposited in the winter. Varves are most often found in lakes that freeze in the winter. The number and nature of varves on the bottom of a lake provide information about the lake's age and geologic events that affected the lake's development.

vein

A long, thin section of a mineral, usually in fibrous form, embedded in rock, called the surrounding rock. Usually caused by the filling in of the mineral in open spaces or cracks in the rock

vent

An opening in the Earth's surface through which lava, gases, and hot particles are expelled. Also called volcanic vent and volcano. Venting is The escaping of hot gases or lava from the crust of the earth.

ventifact

A stone that has been flattened and sharpened by wind abrasion. Ventifacts are commonly found strewn across a desert floor.

verneuil process

The course of creating synthetic gems from molten solutions and letting them form into boules.

viscosity

A fluid's resistance to flow. Viscosity increases as temperatures decrease.

vitreous luster

Luster describing minerals with reflective properties similar to that of glass.

vitriol

Synonym of sulfuric acid.

volatize

Disappear as fumes.

volcanic

Having originated from a volcano.

volcanic arc

A chain of volcanoes fueled by magma that rises from an underlying subducting plate.

volcanic cone

A cone-shaped mountain that forms around a vent from the debris of pyroclastics and lava ejected by numerous eruptions over time.

volcanic crater

A steep, bowl-shaped depression surrounding a vent. A volcanic crater forms when the walls of a vent collapse inward following an eruption.

volcanic dome

A bulb-shaped solid that forms over a vent when lava so viscous that it cannot flow out of the volcanic crater cools and hardens. When a volcanic dome forms, it traps the volcano's gases beneath it. They either escape along a side vent of the volcano or build pressure that causes another eruption and shatters the volcanic dome.

volcanic rock

Rock formed as a direct result of a volcano, the solidifying of magm). See extrusive rock.

volcanism

The set of geological processes that result in the expulsion of lava, pyroclastics, and the volcanic venting effects associated with volcanoes: hot springs, smoking, and fumaroles. Synonym to vulcanism.

volcano

The solid structure created when lava, gases, and hot particles escape to the Earth's surface through vents. Volcanoes are usually conical. A volcano is "active" when it is erupting or has erupted recently. Volcanoes that have not erupted recently but are considered likely to erupt in the future are said to be "dormant." A volcano that has not erupted for a long time and is not expected to erupt in the future is "extinct."

vug

Cavity in rock that is lined with long, slender crystals. A vug forms when air pockets form in cooling magma and allow crystals to form in the hollow area.