Competitive Exams: Geology Glossary S to Z

Geology Glossary: S to Z

  • Sclerometer…Device for the quantitative measuring of hardness.
  • Sedimentary Rocks… Formed originally of sediment, including shale and sandstone, composed of fragments of other rocks deposited after transportation from their sources, and including those formed by precipitation, as gypsum, or by calcareous secretions of animals as in certain limestones.
  • Selvage…The area bordering a vein.
  • Sheen…The iridescence of light reflected from the surface of a stone. Ie: Moonstone
  • Silk…Fine rod like crystals embedded in a crystal
  • Skarn…Contact rock of igneous silicate masses with limestone.
  • Specific Gravity…The weight of a substance compared to the weight of an equal volume of pure water at 4 degrees C.
  • Spectroscope…Instrument which resolves light into its component wavelengths by refraction through prisms or diffraction grating.
  • Spectrum…The band of light showing the succession of rainbow colors corresponding to the different wavelengths. The VISIBLE spectrum is the small portion in the vast spectrum of electromagnetic waves, which extend from very long waves (now used by submarines for underwater communication), to very short waves (gamma) emitted by radioactive elements.
  • Stalactites… Dripstone, stalagmite. The formation of a conelike structure that grows from the deposits of carbonate of lime build up:
  • Star…The effect of proper cutting of a gemstone as a cabochon when the gemstone contains long rod like crystals or fibers in parallel or cavities where these have formally been. The reflection (using a single light source), from the surface produces lines in even numbers, i.e.: 2, 4, 6, 8, 12, with a common center.
  • Step cut… (trap cut). Cut with edges are parallel to those the rectangular table.
  • Synthetic stones…Man made stones which have approx. The same composition and or crystal structure of the natural crystal which they represent (See synthetic diamonds.).
  • Transparency…The degree to which light passes through a substance.
  • Twin Crystals…Two or more crystals which have grown together in a symmetrical fashion.
  • Ultraviolet Light…Wavelengths of light shorter than visible violet light.
  • Ultrabasic rock. Any plutonic igneous rock with very low silica content.
  • Uniaxial…Minerals having single refraction, one optic axis.
  • Vacuolar texture. Texture typical of igneous rocks rich in cavities.
  • Vectorial properties. Properties of a mineral which vary with direction.
  • Vein…A more or less upright sheet deposit of minerals, cutting other rocks and formed from solutions rather than from a molten magma as in a dike.
  • Vicarious elements. Those that take each other's place in trace amounts in a mineral, s crystal structure. Vitreous. Glasslike in appearance or texture.
  • Vug…An open cavity in rocks, often lined with crystals.
  • Xenolith. Rock enclosed in magma.
  • Xrays…Electromagnetic radiations of a shorter wavelength than visible light. Usually less than one Angstrom.