Category Archives: Gemstones

Kyanite

Kyanite

Kyanite

Kyanite’s name derives from the Greek kyanos, meaning “dark blue.” It occurs in metamorphic rocks such as schist and gneiss associated with garnet, staurolite and micas; and in eclogites. The presence of kyanite in rocks indicates that they have undergone moderate temperatures and medium to high pressures during metamorphism. Associated minerals include andalusite, corundum, and staurolite.

 

Kyanite has a vitreous luster, often with irregular streaks. It is difficult to cut because of its variable hardness and cleavage. This variable in hardness is also known as disthene; meaning “double strength,” after the hardness, which is greater across the crystal than lengthwise.

 

The colors of gem-quality kyanite are shades of blue, white, green, gray and occasionally black. It is transparent to translucent and the luster ranges from vitreous to pearly. In jewelry a great deal of bead and cabochon material contains inclusions of quartz, pyrite crystals, hematite flakes and fibers of ilmenite and rutile. It makes a rather brittle gemstone that is susceptible to splitting. It requires careful handling, so any polishing should be done at low speed and ultrasonic and chemical cleaners should not be used. However, it is not sensitive to heat.

 

Kianite can be found in Bahia, Brazil; the St. Gotthard region of Switzerland; Urals in Russia; and Yancy County, North Carolina

 

Kyanite can be confused with aquamarine, benitoite, iolite, dumortierite, and tourmaline; and very often with sapphire.

Jasper

Jasper

Jasper

Jasper is usually considered as chalcedony.  Geologists sometimes put it in a group by itself within the quartz group because of its grainy structure.  The name jasper is derived from the Greek word “iaspis, which means “spotted stone.”  It incorporates various amounts of materials that give it both its opacity and color.  Brick-red to brownish-red jasper contains hematite; clay gives rise to a yellowish-white or gray, and goethite produces brown or yellow.  Jasper is formed through deposition from low-temperature, silicarich waters percolating through cracks and fissures in other rocks, incorporating a variety of materials in the process.

 

Jasper has been used for jewelry and ornamentation since Paleolithic times.  The Babylonians believed that jasper influenced women’s diseases, and was a symbol of childbirth.  The 11th-century Bishop of Rouen, Marbodius, stated that jasper “placed on the belly of a woman in childbirth, relieves her pangs.”  This comes from a time when all stones were believed to be alive and have a sex, jasper being a female stone.

 

Uniformly colored jasper is rare; usually it is multicolored, striped, or flamed.  Sometimes jasper can be grown together with agate or opal.  There is also fossilized material.  It occurs as fillings of crevices or fissures or in nodules.
It is used for ornamental objects, cabochons, and for stone mosaics.

 

There are many names of jasper used in the trade:  Agate jasper (yellow, brown, or green blended, grown together with agate); Egyptian jasper (Nile pebble) strongly yellow and red; Banded jasper (layered structure with more or less wide bands); Basanite (fine-grained, black.  It is used by jewelers and goldsmiths for streak-tests of precious metals); Blood jasper (name sometimes used for bloodstone); Hornstone (very fine grained, gray, brown-red, more rarely green or black.  Sometimes hornstone is understood as a general synonym for jasper); Scenic jasper (brown marking, caused by iron oxide, resembling a landscape); Moukaite (pink to light red, cloudy.  Found in Australia); Nunkirchner jasper (whitish gray, rarely yellow or brownish-red – named after deposits in Rhineland-Palatine), dyed with Berliner blue, misleadingly called “German lapis” or “Swiss lapis” in imitation of lapis lazuli; Plasma (dark green, sometimes with white or yellow spots; and Silex (yellow and brown-red spotted or striped).

 

Deposits of jasper are found in Egypt, Australia, Brazil, India, Canada, Kazakhstan, Madagascar, Russia, Uruguay, and the United States.

Hematite

Hematite
Hematite

Hematite or haematite takes its name from the Greek word haem for “blood,” which describes the color of its powdered form. Hematite is the most important iron ore because of its high iron content (70 percent) and its abundance. The steel-gray crystals and coarse-grained varieties with a metallic luster are known as specular hematite; the thin scaly forms are micaceous hetatite; and the crystals in flower-like arrangements are called iron roses. Hematite is also found as an accessory mineral in many igneous rocks.

 

Much hematite is a soft, fine-grained, earthy form called red ocher, which is used as a pigment. Ancient Egyptians decorated the tombs of pharaohs, with powered hematite, as well as Native Americans that used it for war paint. Egyptians used it for amulets and the Babylonians believed that it would “procure for the wearer a favorable hearing of petitions addressed to kings and a fortunate issue of lawsuits and judgment”. Today it is still used as red ocher pigment and as a metal polishing powder called “jeweler’s rouge,” which is used to polish plate glass and jewelry, and was in the past used to polish gems. Black varieties of hematite were once used for mourning jewelry.

 

The most important hematite deposits are sedimentary in origin, either in sedimentary beds or metamorphosed sediments. Lake Superior in the United States is the world’s largest producer, but other major deposits are found in the Ukraine, China, India, Australia, Liberia, Brazil, and Venezuela. The best cuttable sources come from Cumbria, northwest England; Rhineland-Palatinate, Germany; and the island of Elba, Italy.