GO 340 Gemstones & Gemology
ES 567 Gemstones of the World
Dr. Susan Ward Aber, Geologist & Gemologist
Emporia State University
Emporia, Kansas USA

academic.emporia.edu/abersusa/go340/gb2.htm

Gems in Brief

Many common and some not so common gems are translucent or opaque and fragile or unstable. Therefore visual observations, with and without magnification, are used for identification because common tests for refraction and specific gravity may be inconclusive or destructive. Images and short descriptions below were prepared primarily by students to catalog some of the lesser known gemstones, as well as some common gems too.


Photo date 2/03,
© by S.W. Aber.
Kyanite is an aluminium silicate that is blue to colorless, with a blue-green color most common. The streak is white and gem quality kyanite is transparent to translucent. It has an unusual hardness with two distinct directions, at 4-4.5 and 6-7, based on orientation to the optic axes. The specific gravity is medium high at 3.53-3.70. Kyanite has perfect basal cleavage and also a fibrous fracture and brittle tenacity. It is difficult to cut due to variable hardness and cleavage. The crystal system is triclinic and the gemstone has a vitreous luster. The name kyanite, is a Greek word relating to its blue color. Deposits are found in Myanmar, Brazil, Kenya, Austria, Switzerland, and the United States. (J. Bray)

References: Gemstones of the World, Walter Schumann; Sterling Publishing Co., Inc. New York 1997.



Kunzite (left),Photo date 2/03,
© by S.W. Aber.

Kunzite image (right) taken from
http://www.galleries.com/Kunzite



Hiddenite (left), Photo date 2/03,
© by S.W. Aber.

Hiddenite (right) image taken from:
http://www.galleries.com/Hiddenite

Kunzite and hiddenite are both a variety of the same base mineral known as spodumene, LiAlSi2O6. Thus, they share nearly identical physical properties with the exception of color. They have a hardness rating of 6.5-7 on the Mohs' hardness scale and a specific gravity of 3.1-3.2. Each leaves a white streak. Both of these crystals have a transparent nature with typically high clarity and a vitreous luster. They possess a monoclinic crystalline structure and have perfect cleavage in two directions lengthwise (at nearly 90 degrees). The fracture of the crystals is uneven and brittle. This perfect cleavage along the length of the crystal paired with a brittle tenacity and relatively soft nature of the stone, makes these gems very difficult to cut and facet. Also, each of these gems has a pleochroic nature, which results in differing color intensities depending on the angle of viewing. For example, for these gemstones, the color is much more intense when viewing the crystals from the top or bottom of the prism, along the c axis direction, than when viewing the side of the crystals. The color in these gems is deepest at the top and bottom of the crystal and knowledgeable gem cutters make use of this in crystal selection.

The differences in these two gemstones are caused by differing coloring agents. Hiddenite has chromium as a coloring agent. This creates a green color (varies from yellowish green to emerald green). In contrast, manganese is the coloring agent in Kunzite, which causes a pink-violet to light violet color. There is also a noticeable difference in the fluorescence of the two. Hiddenite has a very weak fluorescence that is yellowish-red, while Kunzite's fluorescence is strong with yellow-red coloring.

All spodumene is found in granite pegmatites. Kunzite can be found naturally occurring in Afghanistan, Myanmar, Madagascar, Pakistan, the U.S. (California and Maine), and is primarily produced in Brazil (Schumann). It was named after G.F. Kunz who first described the gem in 1902. Until fairly recently, hiddenite was thought to be found in only one location: Alexander County, NC (NASFG). However, new deposits have been found in Madagascar, Brazil, Myanmar, and California. Its name derived from A.E. Hidden who found it in 1879. Both of these gems are popular in jewelry. The standard, uncolored variety of spodumene is used as a source of Lithium. (J. Archuleta)

References:


Photo date 3/02,
© by S.W. Aber.

Visit the anorthosite stamp page by Richard Busch!

Labradorite is a gray feldspar showing signature labradorescence (type of schiller). Most common colors of labradorescence are blue and green. The labradorescence is caused by light interference by lattice distortions. It is transparent to opaque with a vitreous luster. Cleavage is perfect, fracture uneven, with a hardness of 6-6.5 and density 2.65-2.75. It is used for jewelry and ornamental objects. Pale transparent stones can be faceted. It is found in Canada, Australia, Madagascar, Mexico, Russia, and the US. (L. Flax)

For additional information on labradorite and larvikite, a Norwegian anorthosite, from R. V. Dietrich (2002), GEMROCKS: Ornamental & Curio Stones, visit:


Photo date 2/02,
© by Berg and Dougan.

Visit the lapis lazuli stamp page by Richard Busch!

Lapis lazuli is a blue rock made up of lazurite, sodalite, hauyne, calcite, and pyrite. The composition varies but the color is usually an intense dark blue with minor veins of white calcite and brassy yellow pyrite. It occurs as boulders or within limestones. The finest quality lapis is from Afghanistan, Argentina, and Chile. It is believed to protect the wearer from evil and has been imitated by stained jasper and glass with copper inclusions. Another imitation is produced by Gilson in France and has a composition similar to natural material. (S.W. Aber)

For additional information on lapis lazuli visit stoneplus.cst.cmich.edu/lapis.htm , R. V. Dietrich (2002). GEMROCKS: Ornamental & Curio Stones.


Photo date 2/02,
© by Berg and Dougan.
Lepidolite is a pink, lilac, or gray mica that is not often used as a gemstone. It has a hardness of 2.5-4 and a medium specific gravity of 2.8-2.9. The cleavage is one-directional and it occurs as sheets or tiny flakes. It is a lithium, aluminum silicate. (S.W. Aber)

Photo date 3/02,
© by S.W. Aber.

Visit the malachite stamp page by Richard Busch!

Malachite is formed from copper containing solutions in or near copper ore deposits. It is a basic copper carbonate and is sensitive to heat, acids, ammonia, and hot water. Aggregates show a banding of light and dark green layers with concentric rings, straight stripes, or other figurative shapes caused by its shell like formation. It occurs in rounded nodules, grape shapes, cone shapes, stalactitic, or rarely, encrusted shapes. It streaks light green and has a hardness of 3.5 - 4. It has perfect cleavage, and its fracture is splintery to scaly. It is translucent to opaque and shows no pleochroism or fluorescence. Malachite was popular with the ancient Egyptians, Greeks, and Romans for jewelry, amulets, and as a powder for eye shadow (ground malachite mixed with ants!). Deposits are in Zaire, Australia, Chile, Namibia, Zimbabwe, and Arizona. (S. Kelley)

For additional information on malachite visit stoneplus.cst.cmich.edu/malachite.htm , R. V. Dietrich (2002). GEMROCKS: Ornamental & Curio Stones.

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Photo date 2/02,
© by Berg and Dougan.

Visit the marcasite and pyrite stamp pages by Richard Busch!

Marcasite is the gemstone name given to pyrite. Marcasite is not stable and will weather to a fine white powder. Pyrite is commonly found all over the globe. Some notable locations of this mineral include Oruro and Colavi, Bolivia; Navajun, Spain; Rio Marina on the island of Elba, Italy; Park City and Salt Lake, Utah; Lake Colorado, Colorado; Alden, New York; Sparta, Illinois. Pyrite has a brassy yellow color and a metallic luster. Pyrite can be found in the isometric crystal system (Bar32/m). The specific gravity of this mineral is about 5.1+ (considered average for metallic minerals). The crystal habits include cube, octahedron, pyritohedron and combination of the three forms. Cleavage of pyrite is very indistinct and a conchoidal fracture is common. The transparency of crystals is opaque. Pyrite has a hardness of 6 to 6.5. The streak is greenish black. (K. Barnett)

Photo date 2/02,
© by Berg and Dougan.
Moonstone gets its name from moonshine (both a shimmery white). It is a potassium feldspar of the orthoclase species. It is colorless, yellow, or has a pale sheen. It gives a white streak and has a hardness of 6 - 6.5. Density is 2.56 - 2.59 and it has perfect cleavage. It is usually cut as a cabochon. Deposits are found in Sri Lanka, Burma, Brazil, India, Madagascar, and the U.S. (S. Kelley)

Photo date 2/02,
© by S.W. Aber.
Moss agate is colorless, translucent chalcedony, having inclusions of green hornblende (or chlorite) that show up in moss-like patterns. The agates' colors are brown and red due to oxidation of the iron hornblende. The name agate is accepted even though moss agate is not the typical banded stone. It is found as fill in fissures and sometimes as pebbles. The best supplies come from India, however, it can also be found in China, Russia (the Urals) and Colorado in the U.S. Usually, it is used in thin slabs to show off the moss-like images, in such things as plates, cabochons for rings, brooches, pendants, and other ornamental objects. It has a hardness of 6 - 7 and a density of 2.58 - 2.64, with a rough fracture and a variable fracture (therefore cannot be used to identify). (P. Mura)


Photo date 3/02,
© by S.W. Aber.

Visit the jade stamp page by Richard Busch!

Nephrite jade is a variety of nephrite that is semitransparent to translucent. It can be white, gray, grayish-blue, grayish-red, grayish-green, brown, lavender, and all shades of green. A rare bluish nephrite jade, called Pacific Blue Jade, is found north of San Francisco, California, USA, as a vein within a serpentine (see the knife and pebble in the image to the left). Factors effecting the price of nephrite jade are, transparency, intensity and evenness of color, and lack of flaws. It has a hardness of 5 to 6, but is very tough due to its fibrous habit. It is often made into beads, earrings and cabochons for rings or pendants, however, it is also often carved into ornamental or religious objects. Nephrite jade is found in Alaska, British Columbia, Wyoming, China, and Siberia. (J. Berg)

The amphibole mineral nephrite (Ca2 (Mg, Fe)5 SI8 O22 (OH)2) is a basic calcium, magnesium, iron silicate (Chesterman, 1979, p. 537). The streak is colorless. The specific gravity ranges from 2.9-3.1 and its fracture is uneven. The name is from the occurrence in Val Tremolo in the Swiss Alps. The applications range from a gemstone to industrial (Chesterman, 1979, p. 538). This Green Good Luck Rock has a medium hardness and is used in jewelry pieces and for carving. In China, jade is especially revered as the surface is smooth and polishes well. Polished jade feels like glass and is somewhat heavy for its relative size. (C. Harris)

References: Chesterman, C. W. (1979). The Audubon society field guide to North American rocks and minerals. NY: Alfred A. Knopf.

For additional information on nephrite visit

  • stoneplus.cst.cmich.edu/nephrite.htm , R. V. Dietrich (2002)
  • GEMROCKS: Ornamental & Curio Stones
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    Return to GO 340 Syllabus or go on to visit more gemstones...

    Gems in Brief A

    Gems in Brief B-C

    Gems in Brief D-J

    Gems in Brief K-N

    Gems in Brief O-R

    Gems in Brief S-Z

    This page originates from the Earth Science department for the use and benefit of students enrolled at Emporia State University. For more information contact the course instructor, S. W. Aber, e-mail: esu.abersusie@gmail.com Thanks for visiting! Webpage created: 2002; last update: September 19, 2012.

    Copyright 1999-2012 Susan Ward Aber. All rights reserved.