Type of cleavage exhibited on a horizontal plane of a mineral by way of its base. Minerals with basal cleavage can sometimes be "peeled". Example = minerals of Mica group.
Basalt is a hard, black volcanic rock with less than about 52 weight percent silica (SiO2). Because of basalt's low silica content, it has a low viscosity (resistance to flow). Therefore, basaltic lava can flow quickly and easily move >20 km from a vent. The low viscosity typically allows volcanic gases to escape without generating enormous eruption columns. Basaltic lava fountains and fissure eruptions, however, still form explosive fountains hundreds of meters tall. Common minerals in basalt include olivine, pyroxene, and plagioclase. Basalt is erupted at temperatures between 1100 to 1250° C.
provide the background upon which thematic data is overlayed and analyzed. As inputs into a GIS, the term base map is usually applied to those sources of information about relatively permanent, sometimes timeless, features including topography, pedology, geology, cadastral divisions, and political divisions. Within a GIS database, such information may become part of a land base to which other information is indexed and referenced.
Harder and usually older igneous and metamorphic rocks that underlie the main sedimentary rock sequences (softer and usually younger) of a region and extend downward to the base of the crust.
Complex, scientific test which is conducted to identify a mineral. A mineral is crushed and mixed into a borax flux, and is heated until a glassy bead forms. The bead is then touched by the crushed mineral powder and one of several colors appears on the bead, depending on the metallic elements of the mineral. The colors are different in most cases when heated with an oxidizing and reducing flame, as well as when the bead is hot and cold.
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