Physical Geology 2004

www.emeralds.com

http://webmineral.com/data/Beryl.shtml

Related Links

The University of Texas at Austin

The Mineral and Gemstone Kingdom

Esmerald.com

Legend of the Emeralds

Mindat.org

Emeralds

Fair speech is more rare than the emerald that is found by slave-maidens on the pebbles - "The Instruction of Ptah-hotep" Oldest known book (Egypt 2500 B.C.)

 

Introduction

Emeralds are one of the coolest and most sought after gemstones on this planet! A rare form of Beryl, Emeralds are known for their green to dark green color and their beautiful gemstone luster. Being prone to flaws, a flawless emerald is a rarety indeed! "A fine qualiity emerald of good color and clarity is so rare that it surpasses a diamond in value" (Burnett). For something so valuable, it is odd that the emerald is mostly useless. It is primarily used in jewelry due to its high refraction rate and its variety of facet-capability. Valued only for its beauty and rarety, this stone exemplifies the sublime beauty of nature and earth for art's sake. They can easily be seen as the most beautiful things on the planet...

 

Beryl Facts

Chemical Formula: Be3Al2Si6O18

Color: Green, Blue, Yellow, Colorless, Pink

Molecular Weight: 537.50 gm

Environment: Mainly granitic pegmatites

Locality: Pala pegmatite District, San Diego Co., California for morganite. Columbia for emeralds. Russia for heliodor.

Name origin: From the ancient Greek, beryllos, signifying a "precious blue-green color of sea water" stone, but through later usage, applied only to beryl.

Crystal System: Hexagonal - Dihexagonal Dipyramidal

Cleavage: Imperfect

Fracture: Brittle - Conchoidal - Very brittle fracture producing small, conchoidal fragments.

Habits: Crystalline - Coarse - Occurs as well-formed coarse sized crystals., Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline)., Columnar - Forms columns

Hardness: 7.5-8

Luminescence: Non-fluorescent

Luster: Vitreous-Resinous

Streak: White

(webmineral.com)

Where Do Emeralds Come From?

"The finest Emeralds come from Muzo and Chivor, Colombia. Fine material has also come from Minas Gerais, Brazil and the Ural Mountains of Russia. Emeralds have also come from the Cobra and Somerset Mines in Transvaal, South Africa, and the Habatchal, Austria. In the U.S., the only significant Emerald deposits are in North Carolina. The most productive and famous locality there is Hiddenite, Alexander Co. Small amounts from North Carolina have also been found in Shelby, Cleveland Co.; Big Crabtree Mountain, Alexander Co.; and Franklin, Alexander Co" (Friedman 2003).

"Gem beryl is found nearly exclusively in hydrothermal veins, pegmatites, or at the contacts of larger igneous intrusions that invade aluminous schist, shale or impure limestone. The volatile fraction of the vein liquid or magma provides Be and the host rock the requisite Al" (University of Texas 1998). Emerald is usually found in hydrothermal veins, though occasionally can be found in pegmatites. In order for the Beryl to form with the dark green coloration of an Emerald, it must be infused with chromium impurities. This process occurs during crystalization and is a very rare occurence. The geological conditions must be just right, including having a source of chromium near the hydrothermal veins. Carbon is a large contributor to how deep the color is. "The scarcity of these emeralds can be comprehended when it is recognized that many of the fine emeralds are those that were found when Pizarro conquered Peru, centuries ago" (Shreve).

Value of Emeralds

An Emerald's value is catagorized by where it comes from, flaws, color, carats, clarity (luster), and cut.

Location: The best emeralds in the world tend to come from either the Muzo or Chivor mines of Colombia. Renowned for their quality, these emeralds tend to have very few flaws and exhibit exceptional coloration and clarity. Zambia is also known for producing quality emeralds.

Flaws: Emeralds are notorious for their tendency towards being flawed. Flaws are conchoidal inclusions, also called "jardines", that are unique to each emerald. The more flaws an emerald has, the less it tends to be worth. Some people, however, prefer a slightly flawed emerald over a flawless emerald because it looks more genuine. Flawless emeralds are so rare that one could easily be suspected of being synthetic.

Colors: The quality of color in an emerald can be seperated into three different catagories: Color, tone, and hue. An emerald's color refers to where its color lies on the color scale. The best color for an emerald is the purest form of green on the color scale. The tone of an emerald lies in how dark or light the coloration is. These range from light to deep intense, with a medium dark green tone being ideal. Hue can be found in how the color appears. You can have a yellowish or bluish hue. The more intense bluish hue is what gemologists look for in a fine emerald.

Carats: The carat of a gemstone refers to its weight. A carat is equal to 200 milligrams. The price of an emerald increases exponentially as size weight increases due to the rarety of the heavier gems. Therefore, an emerald twice the size of another would be worth more than twice the price of the smaller.

Clarity: Clarity is the brilliance and fire that an emerald's unique array of inclusions produce. This array of inclusions is refered to as an emerald's "garden". Clarity is determined using a jeweler's loupe (small magnifying class) at a magnification of 10x. An ideal garden is very, very slightly included to give it the life it needs without being too included.

Cut: The cut of an emerald is fully determinate on how it is processed for jewelry. An emerald's cut is comprised of its shape, brilliance, and polish. The most important aspect of shape is how symmetrical and how deep the cut is. Emerald cuts come in a variety of shapes, including round, princess, oval, marquise, radiant, pear, emerald, heart, square, baguette, and octogan. These shapes determine the brilliance of the cut through the number of facets for each cut. Polishing an emerald smooths facets and defines the edges of facets. Poor polishing can result in streaks or marks on the stone that decreases its value.

(Esmerald.com)

Literature Cited

Shreve, Norris R. Precious and Semi-Precious Jewels--Their Chemical and Beautifying Qualities. Science, New Series, Vol. 92, No. 2399. (Dec. 20, 1940), pp. 566-570.

Williams, Greville. Researches on Emeralds and Beryls.--Part I. On the Colouring-Matter of the Emerald. Proceedings of the Royal Society of London, Vol. 21. (1872 - 1873), pp. 409-421.

Little, Homer P. Discussion and Correspondence: An Ancient Reference to the Emerald. Science, New Series, Vol. 45, No. 1160. (Mar. 23, 1917), pp. 291-292.

http://www.emeralds.com/

http://webmineral.com/data/Beryl.shtml

http://www.geo.utexas.edu/courses/347k/redesign/Gem_Notes/Beryl/beryl_triple_frame.htm

http://www.minerals.net/mineral/silicate/cyclo/beryl/beryl.htm

http://www.esmerald.com/emerald_information.shtml

http://www.mindat.org/min-1375.html

http://www.minerals.net/gemstone/gemstone/emerald/emerald.htm

 

Author: Brian Looney
Creation/revision date: April 20, 2004

Link to other Student Webpages for 2004 Earlham Physical Geology

This website was prepared as an assignment for Geosciences 211 (Physical Geology) taught in the spring of 2004 at Earlham College, Richmond, Indiana.

Earlham College Geosciences Department Earlham Geosciences 211: Physical Geology

Copyright 2004 Earlham College. Revised April 20, 2004 . Send corrections or comments to parkero@earlham.edu