Mineralogy As a discipline, mineralogy has had close historical ties with geology. Minerals as basic constituents of rocks and ore deposits are obviously an integral aspect of geology. The problems and techniques of mineralogy, however, are distinct in many respects from those of the rest of geology, with the result that mineralogy has grown to be a large, complex discipline in itself. Nepheline greasy light graysodalite bluecancrinite yellowfeldspar whiteand ferromagnesian minerals black in an alkalic syenite from Litchfield, Maine, U.
Natural sapphires[ edit ] An uncut, rough yellow sapphire found at the Spokane Sapphire Mine near Helena, Montana Sapphire is one of the two gem-varieties of corundumthe other being ruby defined as corundum in a shade of red. Although blue is the best-known sapphire color, they occur in other colors, including gray and black, and they can be colorless.
A pinkish orange variety of sapphire is called padparadscha. For sapphire, Kashmir receives the highest premium, although Burma, Sri Lanka, and Madagascar also produce large quantities of fine quality gems. For gems of exceptional quality, an independent determination from a respected laboratory such as the GIAAGL or Gubelin of origin often adds to value.
Blue sapphire[ edit ] Teardrop-shaped blue sapphire Gemstone color can be described in terms of huesaturationand tone. Hue is commonly understood as the " color " of the gemstone. Saturation refers to the vividness or brightness of the hue, and tone is the lightness to darkness of the hue.
Blue sapphires are evaluated based upon the purity of their primary hue. Purplevioletand green are the most common secondary hues found in blue sapphires.
Gray is the normal saturation modifier or mask found in blue sapphires. Gray reduces the saturation or brightness of the hue, and therefore has a distinctly negative effect. Dark blue sapphire, probably of Australian origin, showing the brilliant surface luster typical of faceted corundum gemstones.
Sapphires of other colors[ edit ] Sapphires in colors other than blue are called "fancy" or "parti colored" sapphires.
Particolored sapphires cannot be created synthetically and only occur naturally. The deeper the pink color, the higher their monetary value. In the United States, a minimum color saturation must be met to be called a ruby, otherwise the stone is referred to as a pink sapphire. Padparadscha sapphires are rare; the rarest of all is the totally natural variety, with no sign of artificial treatment.
Recently, more sapphires of this color have appeared on the market as a result of a new artificial treatment method called "lattice diffusion". Star sapphires contain intersecting needle-like inclusions following the underlying crystal structure that causes the appearance of a six-rayed "star"-shaped pattern when viewed with a single overhead light source.
The inclusion is often the mineral rutilea mineral composed primarily of titanium dioxide. Occasionally, twelve-rayed stars are found, typically because two different sets of inclusions are found within the same stone, such as a combination of fine needles of rutile with small platelets of hematite ; the first results in a whitish star and the second results in a golden-colored star.
During crystallisation, the two types of inclusions become preferentially oriented in different directions within the crystal, thereby forming two six-rayed stars that are superimposed upon each other to form a twelve-rayed star.
The inclusions can alternatively produce a " cat's eye " effect  if the 'face-up' direction of the cabochon's dome is oriented perpendicular to the crystal's c-axis rather than parallel to it.
If the dome is oriented in between these two directions, an 'off-center' star will be visible, offset away from the high point of the dome.
The gem was mined in the city of Ratnapura, southern Sri Lanka. The value of a star sapphire depends not only on the weight of the stone, but also the body color, visibility, and intensity of the asterism. Color change sapphires are blue in outdoor light and purple under incandescent indoor light, or green to gray-green in daylight and pink to reddish-violet in incandescent light.
Color change sapphires come from a variety of locations, including Thailand and Tanzania. The color-change effect is caused by the interaction of the sapphire, which absorbs specific wavelengths of light, and the light-source, whose spectral output varies depending upon the illuminant.
Transition-metal impurities in the sapphire, such as chromium and vanadium, are responsible for the color change. However, the latter term is a misnomer: This is because genuine alexandrite is a variety of chrysoberyl: If trace amounts of iron are present, a very pale yellow to green color may be seen.
However, if both titanium and iron impurities are present together, and in the correct valence states, the result is a deep-blue color. Because of the valence change there is a specific change in energy for the electron, and electromagnetic energy is absorbed.
The wavelength of the energy absorbed corresponds to yellow light. When this light is subtracted from incident white light, the complementary color blue results.tertiary cultural deposit DEFINITION: A cultural deposit that has been completely removed from its original context and may have been reused.
tertiary flake SYNONYMS OR RELATED TERMS: interior flake, noncortical flake, production flake CATEGORY: lithics DEFINITION: A flake having no cortex. Display More Results Another Dictionary . Open Access Overview. Focusing on open access to peer-reviewed research articles and their preprints.
This is an introduction to open access (OA) for those who are new to the concept. Wisconsin Superintendent of Public Instruction Tony Evers (D) won the Wisconsin Democratic gubernatorial primary.
Evers received percent of the vote to Professional Firefighters of Wisconsin President Mahlon Mitchell's (D) percent..
In the past decade, the Democratic Party of Wisconsin's gubernatorial nominees have been defeated three times by incumbent Gov. Scott Walker (R). Laurentian University (French: Université Laurentienne), which was incorporated on March 28, , is a mid-sized bilingual university in Greater Sudbury, Ontario, Canada..
While primarily focusing on undergraduate programming, Laurentian also houses the east campus of Canada's newest medical school—the Northern Ontario School of Medicine, which opened in Mn/Model Landscape Suitability Models.
Chapter Landscape Suitability Models for Geologically Buried Precontact Cultural Resources. Primary cultural deposits are those which accumulate on the surface from human activity, while secondary cultural deposits are best described as Primary deposits which have undergone modification, either through physical displacement or a change in the use of an activity area.