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McGraw Hill Financial, Inc. is an American publicly traded corporation headquartered in Rockefeller Center in New York City. Its primary areas of business are financial, publishing, and business services.
A hot spring on the ocean floor, where heated fluids exit from cracks in the Earth's crust. Most hydrothermal vents occur along the central axes of mid-oceanic ridges, which are underwater mountain ranges that wind through all of the deep oceans. The best-studied vents are at tectonic spreading centers on the East Pacific Rise and at the Mid-Atlantic Ridge. However, vents are also found over hot spots such as the Hawaiian Islands and Iceland, in back-arc basins such as those in the western Pacific, in shallow geothermal systems such as those off the Kamchatka Peninsula, and on the flanks of some underwater volcanoes and seamounts. Major parts of the mid-oceanic ridges, including those of the Indian Ocean and Southern Hemisphere, are poorly explored, but available evidence suggests that these areas should also have extensive hydrothermal venting. Hydrothermal vent sites, or closely grouped clusters of vent deposits and exit ports, may cover areas from hundreds to thousands of square feet (tens to hundreds of square meters). Individual vent sites may be separated along mid-ocean ridges by more than 1000 mi (1600 km).
Industry:Science
A hybrid science involving the overlap of physics, chemistry, and biology. A dominant aspect of biophysics is the use of the ideas and methods of physics and chemistry to study and explain the structures of living organisms and the mechanisms of life processes.
Industry:Science
A hydrated aluminum silicate with composition Al<sub>2</sub>Si<sub>4</sub>O<sub>10</sub>(OH)<sub>2</sub>. The mineral is commonly white, grayish, greenish, or brownish, with a pearly to waxy appearance and greasy feel. It occurs as compact masses, as radiating aggregates (see <b>illus</b>.), and as foliated masses. Pyrophyllite belongs to the layer silicate (phyllosilicate) group of minerals. The atomic (crystal) structure is similar to that of talc, Mg<sub>3</sub>Si<sub>4</sub>O<sub>10</sub>(OH)<sub>2</sub>, with two of the Mg positions occupied by Al and the third position vacant. The layers are electrically neutral and are held together by weak secondary bonds and long-range ionic (electrostatic) forces. The mineral is soft (hardness 1–1½ on the Mohs scale) and has easy cleavage parallel to the structural layers. The mineral is highly stable to acids. Thermal decomposition begins around 750–800°C (1400–1500°F), and recrystallization to mullite and cristobalite occurs at 1200°C (2200°F) and higher temperatures.
Industry:Science
A hydrated borate mineral with chemical composition Na<sub>2</sub>B<sub>4</sub>O<sub>6</sub>(OH)<sub>2</sub>·3H<sub>2</sub>O. It is monoclinic with symmetry 2/m. It occurs only very rarely in crystals but is found most commonly in coarse, cleavable masses (see <b>illus</b>.) and aggregates. It has two perfect cleavages, (001) and (100), at about 71° to each other, which together produce cleavage fragments that are elongated parallel to the <i>b</i> crystallographic axis. It is colorless to white; colorless and transparent specimens tend to become chalky white on exposure to air with the formation of tincalconite, Na<sub>2</sub>B<sub>4</sub>O<sub>5</sub>(OH)<sub>4</sub>·3H<sub>2</sub>O. The structure of kernite, with space group <i>P</i> 2/<i>a</i>, contains infinite chains of composition (B<sub>4</sub>O<sub>6</sub>(OH)<sub>2</sub>)<sup>2-</sup> which run parallel to the <i>b</i> crystallographic axis. The chains are linked to each other by bonding to Na<sup>+</sup> and by hydroxyl-oxygen bonds.
Industry:Science
A hydrated ferrous phosphate mineral, with the formula Fe<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>·8H<sub>2</sub>O, for which the vivianite group is named. Other important members of this group are annabergite and erythrite.
Industry:Science
A hydrated magnesium layer silicate (phyllosilicate) with composition close to Mg<sub>3</sub>Si<sub>4</sub>O<sub>10</sub>(OH)<sub>2</sub>. Limited substitution of aluminum (Al) or titanium (Ti) for silicon (Si) and of iron (Fe), manganese (Mn), or aluminum for magnesium (Mg) is possible. Steatite is massive talc aggregate that contains less than 1.5% calcium oxide (CaO), 1.5% iron(II) oxide + iron(III) oxide (FeO + Fe<sub>2</sub>O<sub>3</sub>), and 4% aluminum oxide (Al<sub>2</sub>O<sub>3</sub>). Talc commonly is white, but it may appear pale green or grayish depending on the amount of minor impurities. It usually occurs in coarse to fine platy or fibrous aggregates that often have a more or less parallel arrangement. Shreds and plates are often bent; some tabular crystals exhibit perfect basal cleavage, yielding flexible, slightly elastic lamellae. Talc has a greasy feel and pearly luster, and has been used as one of the hardness standards for rock-forming minerals with the value 1 on the Mohs scale. Because talc is soft, it can be scratched by fingernails.
Industry:Science
A hydrated phosphate of aluminum mineral with composition Al<sub>3</sub>(OH)<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> · 5H<sub>2</sub>O, in which small amounts of fluorine and iron may substitute for the hydroxyl group (OH) and aluminum (Al), respectively. Wavellite crystallizes in the orthorhombic system. The crystals are stout to long prismatic, but are rare. Wavellite commonly occurs as globular aggregates of fibrous structure (see <b>illus.</b>) and as encrusting and stalactitic masses. Wavellite crystals range in color from colorless and white to different shades of blue, green, yellow, brown, and black.
Industry:Science
A hydrocarbon or its oxygenated analog containing 30 carbon atoms and composed of six isoprene units. Triterpenes form the largest group of terpenoids, but are classified into only a few major categories. Resins and saps contain triterpenes in the free state as well as in the form of esters and glycosides.
Industry:Science
A hydrocarbon that contains a carbon-carbon double bond (C = C); dienes or polyenes contain two or more double bonds. The synonym olefin is often used, especially in connection with industrial-scale production and applications. The term unsaturated distinguishes compounds such as fats that contain double bonds from saturated molecules that do not.
Industry:Science
A hydrocarbon with a chemistry similar to that of benzene. Aromatic hydrocarbons are either benzenoid or nonbenzenoid. Benzenoid aromatic hydrocarbons contain one or more benzene rings and are by far the more common and the more important commercially. Nonbenzenoid aromatic hydrocarbons have carbon rings that are either smaller or larger than the six-membered benzene ring. Their importance arises mainly from a theoretical interest in understanding those structural features that impart the property of aromaticity.
Industry:Science
