Rare Gemstones: How to Identify, Evaluate, and Care for Unusual Gems
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Rare Gemstones: How to Identify, Evaluate, and Care for Unusual Gems

by Renee Newman
     
 

A full-color guide to identifying, evaluating and caring for rare and unusual gems, including information on their identification properties, history, geographic sources, treatments, imitations, durability, uses, and pricing.

Rare Gemstones provides concise, interesting and practical details on uncommon gems that are now being used by designers to create

Overview

A full-color guide to identifying, evaluating and caring for rare and unusual gems, including information on their identification properties, history, geographic sources, treatments, imitations, durability, uses, and pricing.

Rare Gemstones provides concise, interesting and practical details on uncommon gems that are now being used by designers to create distinctive jewelry. It not only lists the identification properties of the gems, but tells you where they are found, how they are used, why they are unique, how they are priced, and how to care for them. High quality photos show the different colors, cutting styles and varieties of each gem and give you ideas on how it can be used creatively in jewelry. Written in a succinct, user-friendly style, Rare Gemstones is a companion book to Newman's Gemstone Buying Guide and an ideal reference for jewelers, sales associates, appraisers, gem collectors, gemology students, gem dealers and consumers.

The following gems are discussed and illustrated: amblygonite, andalusite, apatite, aragonite, axinite, azurite, benitoite, bixbite, brazilianite, bronzite, calcite, cobaltocalcite, charoite, chrysocolla, cuprite, danburite, diaspore, diopside, dumortierite, enstatite, epidote, fluorite, gaspéite, haüyne, hematite, hemimorphite, howlite, idocrase, jeremejevite, kornerupine, kyanite, larimar, lepidolite, magnesite, marcasite, maw-sit-sit, moldavite, obsidian, pectolite, phenakite, phosphosiderite, prehnite, psilomelane, pyrite, red beryl, rhodochrosite, rhodonite, scapolite, scheelite, seraphinite, serpentine, sodalite, sillimanite, smithsonite, sphalerite, sphene, sugilite, taaffeite, titanite, tugtupite, unakite, variscite, vesuvianite, zultanite.

Some of the distinguishing features of Rare Gemstones are that it:
• Focuses on rare and unusual gems. As a result, the book provides more up-to-date information and photos of these stones than you will find in other general gemstone guides
• Provides retail price ranges for the gems.
• Has 482 photos, many of which show the gems mounted in jewelry, rather than only loose.
• Includes more information on quality evaluation than most other general gemstone guides

Product Details

ISBN-13:
9780929975467
Publisher:
International Jewelry Publications
Publication date:
02/25/2012
Pages:
137
Sales rank:
717,036
Product dimensions:
6.00(w) x 8.90(h) x 0.40(d)

Read an Excerpt

Sample Text from pages 11 & 12

SEQ CHAPTER \h \r 1

Andalusite (and a LOO site), silicates class; andalusite group

Chiastolite; a variety of andalusite

Chemical formula: Al 2 SiO 5 , aluminum silicate. Kyanite and sillimanite have the same chemical composition as andalusite, but different crystal structures.

 

RI: 1.63-1.65 Cleavage: good in one direction, poor in one direction

Birefringence : .007-.013 Hardness: 6.5-7.5; chiastolite 5-5.5

Luster : vitreous, greasy SG: 3.13-3.20 (lower for chiastolite )

Dispersion : 0.016 Optic char: DR biaxial negative; chiastolite: AGG

Fracture : conchoidal Crystal system: orthorhombic

Toughness : Fair to good Crystal shape: slender prisms, waterworn pebbles, massive

Absorption spectrum : not diagnostic, but may show clusters of fine lines around 485 nm to 518 nm, and around 550 nm.

Pleochroism : strong with two or three pleochroic colors in green and orange stones—-typically yellowish green, reddish brown, & yellow or green or colorless.

Fluorescence : inert to LW; may fluoresce weak to moderate green to yellowish green in SW.

Treatments : normally none. It can be heat treated to improve its color, but this is seldom done .

Stable to light; stable to heat unless liquid inclusions are present; no reaction to chemicals.

Ultrasonic cleaning is usually safe, steamer is risky if liquid inclusions are present.

 

 

Sometimes called the "poor man's alexandrite," andalusite often displays two distinct colors face up, which are usually yellowish green and orange. A third yellow color may also be visible. Unlike alexandrite, whose colors change when the lighting is switched from daylight to incandescent lighting, andalusite typically shows two colors simultaneously under the same light. This is because cutters generally orient andalusite to maximize its strong pleochroism, the property of certain minerals to exhibit different colors when viewed from different directions. The contrasting colors create a distinctive looking gemstone. Gem cuts with a long axis such as an oval or rectangle tend to show one color near the center and a second color near the ends; round cuts usually blend the colors into a mosaic. Occasionally, andalusites are cut to emphasize just their orange or pink color .

Andalusite is named after Andalusia, an autonomous community in Spain where it was first discovered. A translucent variety that has graphite inclusions forming a cross is called chiastolite. The name is from the Greek chiastos , meaning "arranged diagonally" because the pattern of carbon inclusions resembles the Greek letter chi, which is written "ϰ." Chiastolite is sometimes cut as amulets in countries such as Spain, where the symbol of the cross has deep religious significance. Because of impurities, chiastolite may have a lower hardness and density than transparent stones.

Most gem-grade andalusite is from Brazil in the states of Minas Gerais and Espirito Santo. Sri Lanka and Myanmar are minor sources. Chiastolite is mined in China, South Australia, Spain, Siberia, Myanmar, Zimbabwe, and California, Pennsylvania and Maine in the U.S. In recent years, large quantities of excellent chiastolite have been coming from Hunan province, China.

Despite its rarity and unique appearance, prices of andalusite are relatively low. Retail prices for extra fine andalusite above five carats seldom surpass $500/ct. Low-quality material less than three carats may sell at prices below $20/ct. The retail range of eye-clean andalusite about one carat in size is roughly $50/ct to $300/ct.

According to dealer Simon Watt, the finest andalusite would be orange-brown and olive-green with flashes of pink, but preferences vary. The tone (lightness / darkness) and saturation (intensity) is more important than the actual hue (e.g., orange, yellow, green, pink, etc.). Very dark or very light stones generally cost less than more colorful ones in medium to medium-dark tones. Unlike gems such as sapphire, where pleochroism may be a negative factor, it is desirable for andalusite to display more than one color in the face-up position. Clarity and transparency are important factors that can determine whether a stone is industrial, commercial, or fine quality. Highly included material can sell for less than $5.00 per carat. The quality of the cutting also affects price because good cutting requires more time and usually results in a greater loss of weight from the rough. But it is worth the additional cost because the result of proper cutting is greater brilliance and a better display of color.

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