Optical Mineralogy

The Polarizing Microscope

suze08 — Mon, 01 Mar 2010 10:19:16 +0000

The polarizing microscope is also known as the petrographic or petrological microscope. Polarizing microscope is the principal piece of equipment used by geologists and mineralogists to observe the optical properties of minerals. There are actually numerous microscopes available on the market today but petrographic polarizing microscopes are the most significant kind that is commonly used in optical mineralogy. Several microscopes vary considerably in their construction details. This applies particularly to the illumination and sub-stage condenser systems of the polarizing microscope. Some of these are designed for routine and uncritical work while others require adjustments to be made. It is therefore important to note that one must know how to correctly adjust these systems for the particular microscope being used. (more…)

Chalcedony

suze08 — Mon, 01 Mar 2010 10:16:11 +0000

The chemical formula of mineral Chalcedony is indicated by SiO2 or Silicon Dioxide. Chalcedony actually occurs in every imaginable color that appears more fascinating under polarizing light microscope used in optical mineralogy. Chalcedony is commonly found leaving a white streak when rubbed on a white porcelain streak plate. The hardness measure of the mineral when it is evaluated using the Mohs scale method is usually 7. Chalcedony is known to crystallize in the hexagonal system of crystal formation. In optical mineralogy, the hexagonal system of crystallization comprises crystals having four axes. Three of which are positioned in a single plane with equal length and are symmetrically spaced. The fourth axis is found to be perpendicular to the other three axes. It is however important to note that Chalcedony, being a microscrystalline variety of quartz does not occur in crystals. It is commonly found occurring in botryoidal, mammilary, stalatitic, massive, nodular, as smooth rounded peebles, as banded, and in geodes. Most Chalcedony crystals are found transparent to opaque in appearance. The specific gravity measure of Chalcedony is usually found ranging from 2.6 to 2.7 grams per cubic centimeters. (more…)

Celsian

suze08 — Mon, 01 Mar 2010 10:14:03 +0000

The chemical formula of Celsian is indicated by BaAl2Si2O8 or Barium Aluminum Silicate. Celsian belongs to the Silicates Group of minerals. It is sometimes found with some calcium and potassium. Celsian is usually found forming a solid solution series with Orthoclase and the intermediary member is hyalophane. Celsian is most commonly found colorless, white, light yellow, reddish, brownand sometimes gray, all of which can be very interesting and fascinating when evaluated or viewed with the aid of petrographic polarizing light microscope used in optical mineralogy. Celsian is most commonly found leaving a white streak when rubbed on a white porcelain streak plate. The hardness measure of Celsian is only 0.5 and it is usually found occurring in short tabular crystals and long slender prisms. It is actually known to crystallize in the monoclinic system of crystal formation. In optical mineralogy, the monoclinic system of crystal formation comprises crystals having three axes of unequal lengths. Two of which are usually found in a position that is oblique or not perpendicular to one another. However, both of which are commonly found perpendicular to the third axis. Celsian also occurs acicular and massive in form. The specific gravity measure of the mineral is usually ranging from 3.1 to 3.4 grams per cubic centimeters. It is usually found showing a vitreous to greasy luster when viewed in reflected light of polarized microscope used in optical mineralogy. (more…)

Agate

suze08 — Mon, 01 Mar 2010 10:10:29 +0000

The chemical formula of Agate is indicated by SiO2 or Silicon Dioxide. Agate is actually a banded, multicolored, variety of Chalcedony. It is most commonly occurring in an infinite amount of color and patterns. It is also important to note that, no two Agates are alike. The extraordinary beauty and uniqueness of Agate is responsible for its great popularity. Agate, however, must be polished well to bring out its full charm and splendor. This is so because unpolished specimens are dull and ugly. It usually forms in rounded nodules or knobs which must be sliced open to bring out the internal pattern hidden in the stone. Agate is usually found leaving a white streak when rubbed on a white porcelain streak plate. The hardness measure of the mineral when it is evaluated using the Mohs scale method is usually 7. Agate is known to crystallize in the hexagonal system of crystal formation. In optical mineralogy, the hexagonal system of crystallization comprises crystals having four axes. Three of which are positioned in a single plane with equal length and are symmetrically spaced. The fourth axis is found to be perpendicular to the other three axes. It is however important to note that Agate, being a microscrystalline variety of quartz does not occur in crystals. It is commonly found occurring in botryoidal, mammilary, stalatitic, massive, nodular, as smooth rounded peebles, as banded, and in geodes. Most Agate crystals are found transparent to opaque in appearance. The specific gravity measure of Chalcedony is usually found ranging from 2.6 to 2.7 grams per cubic centimeters. (more…)

Aerugite

suze08 — Mon, 01 Mar 2010 10:07:38 +0000

The chemical formula of mineral Aerugite is indicated by Ni9As3O14. Aerugite is found in the walls of furnaces used to roast ore. It is actually usually found at its type of locality at South Terres Mine, St. Austell, Cornwall, England. Aerugite was named for the Greek word for copper rust, an allusion to its appearance. Aerugite is known to crystallize in the trigonal-hexagonal system of crystal formation. In optical mineralogy, the hexagonal system of crystallization comprises crystals having four axes. Three of which are positioned in a single plane with equal length and are symmetrically spaced. The fourth axis is found to be perpendicular to the other three axes. (more…)

Afghanite

suze08 — Sat, 27 Feb 2010 09:35:41 +0000

The chemical formula of mineral Afghanite is indicated by (Na, Ca, K)8(Si, Al)12O24(SO4, Cl, CO3)3-(H2O). Afghanite is actually generally associated with the sodalite-group minerals. It is found in its type of locality at Sar-e-Sang luzurite deposit in Afghanistan. It was named after its type of locality. Afghanite is known to crystallize in the hexagonal system of crystal formation. In optical mineralogy, the hexagonal system of crystallization comprises crystals having four axes. Three of which are positioned in a single plane with equal length and are symmetrically spaced. The fourth axis is found to be perpendicular to the other three axes. Afghanite is most commonly found blue or colorless in color that appears more fascinating when viewed with the aid of petrographic polarizing light microscopes used in the field of optical mineralogy. (more…)

Aerinite

suze08 — Sat, 27 Feb 2010 09:31:27 +0000

The chemical formula of mineral Aerinite is (Ca, Na)6FeAl(Fe+, Mg)6[Si12O36(OH)12H][(H2O)12(CO3)]. Aerinite is actually an alteration product in basalts and andesites as well as in hydrothermal zeolite deposits. It is usually found in its type of locality at Aragon, Caserras, Spain and St. Pandelon, Landes, Spain. Aerinite was named from the Greek word root aer, alluding to the atmosphere or sky and hence the color, sky blue. Aerinite is known to crystallize in the trigonal system of crystal formation. (more…)

Aenigmatite

suze08 — Sat, 27 Feb 2010 09:27:54 +0000

The chemical formula (Na, Ca)4(Fe++, Ti, Mg)12Si12O40. A primary constituent in sodium-rich alkali volcanic, pegmatites, and other silica-poor igneous rocks. Aenigmatite notably occur at localities including Naujakasik, near the Tunugdliarfik Fjord, and on the Kangerdluarssuk Plateau, in the Ilimaussaq intrusion; from Narssarssuk; and elsewhere. The name of the mineral Aenigmatite was derived from the Greek word for riddle, apparently an allusion to its formerly uncertain chemical composition. The mineral is known to crystallize in the triclinic system of crystal formation. In optical mineralogy, this triclinic crystal system commonly comprises crystals having three axes, of which all are unequal in length and are positioned oblique to one another. Mineral Aenigmatite is usually found showing perfect cleavage in one direction which can be seen more clearly exhibited when viewed with the aid of polarizing light microscope used in the optical mineralogy. Mineral Aenigmatite is usually found exhibiting brown or black color. The specific gravity measure of the mineral is usually ranging 3.74 to 3.85 grams per cubic centimeters. Most crystals of mineral Aenigmatite are found opaque in appearance. They are also most commonly found forming lamellar crystal forms or thin laminae producing a lamellar structure. The hardness measure of the mineral when it is evaluated using the Mohs scale method is between 5 to 6. This mineral is non-fluorescent and it is usually found showing subadamantine luster when viewed in reflected light of polarizing microscopes used in optical mineralogy. Aenigmatite is most commonly found leaving a reddish brown streak when specimen is rubbed on a white porcelain streak plate. Aenigmatite is also commonly found showing biaxial positive figure when viewed between crossed nicols of polarized microscopes.. The birefringence of the mineral is usually found 0.0900 to 0.1000. The dispersion angle is usually between 27- to 55-degree. Aenigmatite is usually found pleochroic in light brown, brown to dark brown color. Aenigmatite is a non-radioactive mineral.

Abswurmbachite

suze08 — Sun, 14 Feb 2010 11:27:39 +0000

The chemical formula of mineral Abswurmbachite is indicated by Cu++Mn+++6SiO12. Abswurmbachite is most commonly found in very low-grade, high pressure metamorphic Mn, Al-rich sediments. Abswurmbachite is most commonly found at its type of locality at Milli, Avia and Andros Island, Greece. Abswurmbachite is named after the German mineralogists, Irmgard Abs-Wurmbach. Abswurmbachite is known to crystallize in tetragonal system of crystal formation. In optical mineralogy, this tetragonal system comprises crystals having three axes, which are all in a position perpendicular to one another. Two axes are usually found having the same or equal length. (more…)

Abenakiite-(Ce)

suze08 — Sun, 14 Feb 2010 11:24:56 +0000

The chemical formula of Abenakiite-(Ce) is indicated by Na26REE6(SiO3)6(PO4)6(CO3)6(SO2)O. Abenakiite-(Ce) was named for the Abenaki Indian tribe, which inhabited the area around Mont Saint-Hilaire. Abenakiite-(Ce) is usually found as a single crystal that is embedded in sodalite in a xenoliths of sodalite syenite. Abenakiite-(Ce) is known to crystallize in the trigonal-hexagonal system of crystal formation. In optical mineralogy, the hexagonal system of crystallization comprises crystals having four axes. Three of which are positioned in a single plane with equal length and are symmetrically spaced. The fourth axis is found to be perpendicular to the other three axes. The type of locality of Abenakiite-(Ce) is Poudrette Quarry, Mont Saint-Hilaire, Rouville County, Quebec, Canada. (more…)