10 posts in this topic
By Steve Herschbach
A CONTRIBUTION TO ECONOMIC GEOLOGY (1957)
GEM STONES OF THE UNITED STATES
By Dorothy M. Schlegel
Many semiprecious, but few precious, gem stones have been found in the United States. Beauty, durability, and rarity are the most important qualities of a precious gem. Gem stones are distinguished by their physical properties: color, crystal form, cleavage, parting, hardness, specific gravity, luster, index of refraction, transparency, and dispersion. Gems are named for their color, type locality, outstanding physical property, or persons. The most popular gem cuts are the cabochon, rose, brilliant, step, and mixed. The carat, one-fifth of a gram or 200 milligrams, is the unit of weight measurement. The color of four popular gems may be changed by heat treatment or dyeing. Only the ruby, sapphire, spinel, emerald, rutile, and quartz of gem quality have been synthesized. The best quality of assembled stones are the doublet and triplet. Most gem stones are found in alluvial gravels and igneous rocks, especially granite and pegmatite deposits.
Gem stones generally are divided into two categories: precious and semiprecious. A precious gem stone has beauty, durability, and rarity, whereas a semiprecious gem stone has only one or two of these qualities. The diamond, emerald, ruby, and sapphire are considered precious gems. Some opal is precious, but most varieties are semiprecious.
The beauty of a gem stone is determined by personal taste. In ancient times man preferred brightly colored, translucent or opaque stones. Today he prefers evenly tinted, transparent stones. The desired hues are blue, rose, green, and true canary yellow in the diamond; pigeon-blood red in the ruby; cornflower blue in the sapphire; and grass green in the emerald. Most diamonds, however, are colorless.
The durability of a gem stone depends upon its hardness and lack of ready cleavage. A gem must be sufficiently hard to resist abrasion by objects normally found in everyday life and by dust. It should also resist the chemicals with which it comes in contact. Cleavability is the tendency of certain gems to split in one direction more readily than in another.
Rarity is one of the most important factors in establishing the price of a gem stone. Such gems as the diamond and ruby are rare, in addition to being beautiful and durable, and therefore are very expensive. Although the deep red pyrope garnet closely resembles the ruby in color, there is no comparison in expense and popularity.
The purpose of this report is to give the amateur gemmologist some of the important information available on the gem stones of the United States. Although the finest precious gems occur in foreign countries, a wide variety of semiprecious stones, and a few precious gems, have been found in the United States. About 50 major gems and the geology of their occurrence are described in this report. William F. Foshag, U. S. National Museum, has kindly reviewed the manuscript and made many valuable suggestions. Dana's "A textbook of mineralogy" is the source of the chemical formulas.
Full text PDF here
By Steve Herschbach
"A rare diamond known as the Pink Star has been sold in Hong Kong for more than $71m (£57m), setting a new world record for any gemstone at auction. The oval-shaped 59.6 carat stone was bought after just five minutes' bidding at Sotheby's, reports said. It is the largest polished diamond in its class to go under the hammer. It sold for $83m in Geneva in 2013 but the buyer later defaulted. The record until now was held by the Oppenheimer Blue, which sold for $50m last May."
Details and photos here.
Can you recommend any places that would be good in Alaska. I think copper is much prettier than any other metal, having a few nuggets to put in the display would be neat!
Years ago I found a small copper nugget about the size of a 22 bullet at Matanuska glacier, sure liked that little nugget. Ended up putting it in a small vial of gold,
Sometime later I sold a spiral panner to a lady with a handicapped son. He really liked prospecting and she thought it was really helping him with his disability. She told me they were not having good luck finding gold and didn't know the difference between gold and fools gold. Well I marched rite into the house grabbed a vile of gold and gave it to her!
She really appreciated that and I felt good about myself until I realized that 1/4 oz of gold also had that little copper nugget in it. Still irritated about that!
Many years ago I bought this 105 grammer on ebay and it came out of the United States. I don`t know if this nugget is natural or tumbled and the glossy side has never dulled so I guess its got some kind of varnish on it. I`ve also got a 16 ouncer somewhere in the house that is all jagged and rough with green bits all over it.
Does anybody detect for copper in the States, does copper only come out of mines, or can copper just be lying around on the ground? cheers Dave
Sunday, and i should go hunt for something...
there are rocks out there not in the fields in the USA, but they can be found in shops and rummage sales as items carried home by travelers from exotic lands. the stone I'm referring to is a very special white jade found in a specific area in China. the jade is hetian nephrite and comes from an area in Xin Jiang, China very near Turkey. it is easily confused with other white nephrites and tons of other white jades are passed off as hetian, the differences in the materials are slight, but the difference in value is tremendous.
the most valuable of the hetian jades and most highly prized by collectors are fatty pure white specimens found in river beds with the outer matrix worn off by the action of the water and surrounding gravels. the very highest quality hetian nephrite will fetch in the neighborhood of $1000.00 per gram US dollars. This jade has been prized for centuries and spurred a movement of sorts not unlike California's gold rush, the entire area is now off limits and under state protection from the ravages of collectors.
The gold nugget is 9.5 grams and the little jade fish is 5.2 grams, the nugget is worth in the $400. range depending on the buyer this little fish from the studio of Xio Fan in Suzho, China would bring close to $10,000.00 (or a new GPZ) from a knowledgeable buyer. in the second picture is another hetian pebble of aprox 30 grams a slightly lesser quality, but showing very good skin, alongside the little fish for comparison. the slight differences in color and clarity drop the value by as much as 1/2 of the top quality per gram.
so if you are out hunting in in odd shops and come across a curious little white rock some traveler carried home from vacation???