Allano's Gemstone Guide

By Allan Taylor

Allano explains how much can be done to identify gemstones using simple equipment such as a loupe, polariscope, dichroscope, magnet and Chelsea filter. Much more equipment is needed to solve the problem of distinguishing between synthetic and natural gemstones, including emerald, ruby, alexandrite and quartz, which is well covered with up-to-date information on what is on the market today.

Simulants of diamond, emerald and tanzanite are studied as are the more popular natural gemstones tourmaline, topaz , aquamarine, garnet, and jade.

Present day production of gemstones from East Africa, from Kenya to Zambia and Madagascar is reported on, together with a gemstone safari in Zimbabwe. How to use one's knowledge of gemstones to prospect for other minerals is explained as an application of micro-gemology

• Language: English
• Publisher: Allan Taylor
• Release date: Oct 19, 2013
• ISBN: 9781301919802

Allan Taylor

Allan Taylor (Allano) is a travel writer and blogger. He was born in Palmerston North, New Zealand and in NZ attended Otago and Victoria Universities majoring in chemistry, geology and economics. Later he went on to Pennsylvania State University, USA, to do a PhD degree in Geochemistry. Allano now lives in Adelaide, South Australia, and enjoys the wonderful wine and Mediterranean climate. Allano has traveled throughout Australasia, Central and South America and Africa. His favorite countries to write about are Mexico and Chile. Other topics of interest are gemstones, trout fishing, cooking and politics.

Book preview

Allano's Gemstone Guide

By Allan Taylor

Table of Contents

Introduction

Use in gem identification: loupe * dichroscope * chelsea filter * fluorescence * magnetism * diamond tester

How to identify a loose gemstone

Testing for synthetic and natural gemstones:

emerald * ruby * alexandrite * quartz

All about simulants of: diamond * emerald * tanzanite

All about: tourmaline * garnet * aquamarine * topaz * peridot

cat's eye * jadeite * Paraiba tourmaline

Gemstones of East Africa * Zambia and Zimbabwe

Gemstone Safari in Zimbabwe

Making Gemstone Bead Jewellery

Prospecting for Gemstones

Gold pan prospecting for heavy minerals

Conclusions

Bio

Copyright 2013 Allan Taylor

Smashwords Edition

License Notes

This ebook is licensed for your personal enjoyment only. This ebook may not be re-sold or given away to other people. If you would like to share this book with another person, please purchase an additional copy for each recipient. If you are reading this ebook and did not purchase it, or it was not purchased for your use only, then please return to Smashwords.com and purchase your own copy. Thank you for respecting the hard work of this author.

Photo Attribution

Cover Image: Photo taken by Cliff 1066 of Arlington, Virginia,. sourced from Wikimedia Commons. This is the Hooker Emerald brooch located now in the Smithsonian Institute. A superb 75 carat Colombian emerald is surrounded by 129 diamonds, totalling 13 carats. The emerald was originally worn in the belt buckle of Abdul Hamid II, Sultan of the Ottoman Empire, 1876 - 1909.

Introduction

This is a collection of 28 gemstone related articles (ca. 36,000 words) that I have written for magazines, newspapers and newsletters in the past. Now they are presented for modern viewing and retrieval from cyberspace. The electronic book is how it is done today which was not feasible a decade ago. A lone print article when aggregated with others, allows them to acquire a synergy and new usefulness to the reader. Articles begin with a centered title and end with a &&& mark.

Gemology is a large field of study. This ebook covers only those aspects that I have been involved in. Always I have collected minerals and gemstones and have wondered how they form in nature. Here are some of my observations and answers to this mystery.

Use of the binocular microscope, refractometer and spectroscope, which are major tools of the gemologist, is explained particularly when distinguishing between synthetic and natural gems. Together with this detailed scientific material are fun articles containing much information on simple tests and observations that can be done by gemstone enthusiasts having limited equipment.

How to use a loupe

A loupe is a jeweler’s name for a little magnifying glass of about 10x power. Of more general use is a combination double hand lens set of 10x and 20x magnification used by gem and mineral enthusiasts and field geologists.

To identify a gemstone by using a loupe, or hand lens, is quite a challenge. Success depends on your knowledge of gemology and your experience in handling gemstones. Usually, one tries to bring together additional information from further testing if possible, such as dichroism, refractive index, specific gravity, fluorescence, absorption spectra etc., which considered in aggregate should result in a definitive result.

However, what can be achieved with a hand lens alone? An interesting question, for many of us may not possess the useful, and more expensive gem testing equipment, or, if the gemstone is set in jewelry there may be little else you can do but examine it with a loupe.

Gemstone enthusiasts and gem cutters always have a little collection of the most common gemstones as loose specimens, nicely faceted or cabochon cut. They are your friends. They are very important for reference material when confronted with an unknown specimen, either as a loose gem or one set in jewelry.

You must be familiar with ruby and sapphire (natural and synthetic), the quartzes (amethyst & citrine), aquamarine and emerald, blue and yellow topaz, peridot, chrysoberyl, the many colored tourmalines, zircons, garnets, and various common synthetics such as spinel, corundum, cubic zirconia, plus the pastes (glass) and doublets. Instead of watching television at night try playing around with your gemstone collection and get to know your friends!

It is much easier to identify a loose gemstone than one set in jewelry because with the latter you are greatly limited as to what testing is possible. Now the hand lens and your knowledge of gemology is to the forefront. Some practical examples: let’s say your lady friend presents you with her treasured grandmother’s gold ring with a 4 mm central brilliant cut red stone flanked by smaller diamonds?, and asks you whether these are real gemstones and is the ring valuable? Not only do you have to be a gemologist who knows his stuff and limitations, but also sometimes you have to be a diplomat and express puzzlement or inadequate knowledge.

A small faceted round red gemstone would at first guess be a ruby (natural or synthetic), although possibly a garnet? (is it the right color?), or maybe a zircon, or even a tourmaline? What to do? Using a hand lens you can check out how well the gem is cut and polished. If the faceting is well done then you can suspect the stone is valuable. Being a small gem and set in a ring it may not be possible to see any internal features, or indeed, measure its refractive index, even if you had a refractometer.

My next step would be to bring out my pencil blue LED light to see if the gem fluoresces red, as do all synthetic rubies and many natural ones. Under blue or UV light rubies glow red (absorb blue energy and emit (and transmit) red light. The other possibilities (garnet, zircon, tourmaline) do not do this and remain dull, or non-fluorescent. A red fluorescent glow is also seen with synthetic flux-grown emeralds (Chatham and Gilson) and the former Linde hydrothermal emeralds, provided the were grown in an iron-free environment, since traces of iron quenches the effect, as it does in natural emeralds.

It is necessary to take a systematic approach to the problem of identification, which depends on whether the gem is set in jewelry, or loose (easier), and on what testing equipment you have.

Eye-ball approach: You can observe the gemstone and note its color (e.g., shades of red, shades of green, shades of blue etc. Record size and shape of stone and cut (e.g., 8 x 10 mm cushion cut, or 10 mm round brilliant etc). This is a start.

Next: What optical properties can you estimate by looking at it? Refractive index (RI), dispersion, double/single refraction and dichroism? Hey, wait a minute, I can’t do that without any equipment, you may say! Yes, you CAN estimate values and say whether they are low, medium, high or very high, by comparison with your standard gem samples in your collection of known specimens.

For example: A colorless gemstone is set in a ring. Compare it with a known cut quartz, beryl, topaz, diamond, zircon, cubic zirconia (CZ), rutile etc. You estimate low RI (low reflectivity) and no dispersion (no fire or rainbow colors) then you suspect quartz, beryl or maybe paste. Moderate RI (better than quartz) but no fire, suspect topaz, synthetic corundum or spinel, or paste. You estimate high RI and noticeable fire, suspect diamond, zircon, CZ (if exceptionally gaudy fire suspect rutile).

Colored gemstones provide more clues for identification. The shade of color can be distinctive if you are familiar with your reference gem collection. Peridot is nearly always peridot color like asparagus is always asparagus green. Peridot has appreciable double refraction and by using a hand lens you may detect this as a doubling image of the back facets, where they join up. This detection of double refraction with a hand lens is useful to determine the gem as definitely not isotropic, or of cubic symmetry.

Green tourmaline, olive variety, is frequently encountered in jewelry and when not too dark is an attractive gemstone in step cut and fancy shapes. The gem cutter can spot them a mile away because of their distinctive color, strong dichroism and the need to have correct crystal orientation to get the brightest result, as with all colored tourmalines.

Natural tourmalines usually come in elongated trigonal prisms which exhibit strong dichroism, no matter what color, which includes most colors. The olive green prisms are always cut with the table facet parallel to the C-axis or prism direction to get the lightest color. The O-ray is very strongly absorbed, which is the light traversing the length of the prism. Olive tourmalines, when conventionally cut, will have noticeable dark regions at the ends of a rectangular shaped stone because of the high light absorption of the O-ray. However, a clever gem cutter can deliberately avoid this by having vertical end facets on the pavilion of the gem! The pale colored tourmalines (e.g., pink and yellows etc) will be orientated in the opposite direction, with the table facet parallel to the basal plane to get maximum color, which means usually a round or oval small gemstone. When viewed sideways, dichoism (two colors) may be detected using a dichroscope or polaroid lens.

Red garnets show a distinctive range of colors from almandine (dark red to purplish), rhodolite (rose red), spessartite (orangy red), pyrope (ruby red) etc., and then you have the rare green ones. They are all isotropic (no double refraction) and do not fluoresce (high iron content) and when loose the iron and manganese rich ones are noticeable magnetic, unlike ruby. Small faceted garnets (pyrope, almandine, spessartite) can be dragged around and picked up by a strong neodymium magnet.

To examine the internal features of a gemstone with a lens, there are two ways of doing it. Such features may include color banding, wisps of fluid inclusions, gas bubbles, needles and granular inclusions, doublets etc., which may help in identification.

Immerse the stone in a liquid, such as a cooking oil (RI 1.47) which allows easier viewing. I use the base of 50 ml glass beaker to contain things. Look at the stone side on. Color banding and doublets are detectable. Also an estimate of refractive index is possible. Shine a light (LED) down on top of the gems which are sitting on their table facet, together with a few known gemstones from your collection. The cut gems, because of their shape, act as magnifying glass and concentrate the light to form a lower image on white paper below. The images have a bright area with a black rim, the latter being wider as the refractive index becomes greater than the oil. Quartz and

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