Properties of Hauyne from the Eifel district, Germany

Properties of Hauyne from the Eifel district, Germany

Approximately one-third of 100 samples submitted to our laboratory (and a smaller proportion of the other samples) showed orange fluorescence to long-wave UV radiation; the remaining samples were inert. When fluorescence is observed, it is considered characteristic of hauyne from the Eifel district. The inconsistency in fluorescence reaction that we observed was also mentioned by Bank. Most of the hauynes showed a very weak reddish fluorescence to short-wave UV.

The pyrope crystal has a round shape formed by rough trapezohedron face. The crystals are heavily fractured and always covered by a thin layer of white to pale green phengite. Some of the pyrope crystals contain clear portions that can be faceted into attractive gemstones. The faceted pyropes were purple to purplish pink in hue, with very low to moderate saturation. In many gems, the color was not homogeneously distributed. All of our samples showed some color (in both fluorescent and in candescent light), although near-colorless gem pyrope is known from the Brossasco area.

The refractive indices ranged from 1.717 to 1.730, with the lowest values measured on the palest samples. The range of R.I. values obtained correlates to the iron content (manganese is close, and chromium is below the detection limit of the electron microprobe for these elements, which is 0.02 wt.% oxide). Specific gravity ranged from 3.58 to 3.67; in general, the lowest values were obtained for the palest stones. The lowest value is identical to that reported in the literature for a near-end member pyrope. The highest S.G. values correspond to the greatest concentrations of iron. However, some gemstones with a moderately intense purplish pink color contained abundant heavy inclusions (rutile), which prevent a straightforward correlation between specific gravity and chemical composition. All of the samples were inert to both short- and long-wave UV radiation.
Australian opal

Natural opal is amorphous, that is, non-crystalline silica (silicon dioxide, similar to quartz and sand) in a rigid gel form containing between about 5 and 9 % water. It has a refractive index of about 1.46, a specific gravity between 2.10 and 2.13, and a Mohs’ scratch hardness a little greater than 6, which is between moonstone and quartz.

The unique play of colours characteristic of gem opal is not due to the effects of trace elements, as with ruby, emerald or sapphire, but is caused by a most unusual structure at the submicroscopic scale developed during its genesis. This structure consists of myriads of minute silica spheres cemented together by a silica gel. The diameters of the spheres therefore determine the maximum size of the wavelength or colour that can be developed, with reds requiring the largest spheres, decreasing through orange and green to blue which requires the smallest spheres. All colour (wavelengths) mixed together constitute white light. The greater the range of sphere diameters, the more intensively white, opaque or “potchy” the stone becomes, and the less intense is any colour display. Potch from Lightning Ridge is often deeply pigmented and opaque grey to black, and is invariably the underlying base to the best gem quality black opals.

Дополнительный словарь:

hauyne – гаюин	inconsistency – несовместимость
similar – подобный	purple – пурпурный, багровый
evenly – равномерно, одинаково	homogeneous – однородный
to cite – ссылаться, цитировать	candescent – светящийся
to submit – представлять	close – близкий
to remain – оставаться	to obtain – получать, достигать
abundant – обильный, богатый	myriad – бесчисленный
straightforward – прямой	therefore – следовательно, поэтому
rigid – твердый, жесткий	to mix – смешивать
unique – уникальный	invariable – неизменный

6.10. Answer the questions:

1. What minerals are visually like hauyne?

2. What group of minerals is pyrope belonging to?

3. May pyropes from Italy used as gemstones?

4. Are physical properties of pyrope correlated with its chemical composition?

5. What chemical composition has opal?

6. What hardness has opal?
6.11. Which of the listed below statements are true/false?

1. Hauyne from Germany differs from the literature data on physical properties.

2. Some samples of hauyne show orange fluorescence to long-wave UV radiation.

3. Pyropes from Italy have purple colour and sometimes pink one.

4. Variation of physical values of pyrope depends on iron presence.

5. The unique play of colours of gem opal is due to presence of different inclusions.

6. The hardness of opal is between moonstone and quartz.

7. The precious opal is containing more 20 % water.

These is a variety of features contained within a gemstone:

Inclusions are often given descriptive names:

1. foreign bodies

2. solid particles

3. virtually colorless

4. liquid-gas inclusions

5. needle-like growth channel

1. What inclusions are protogenetic called?

2. What inclusions are syngenetic called?

3. What inclusions are epigenetic called?

3. 
   In what gem is horsetail observed?
   

1. капельки водных растворов

2. различные типы трещин

3. серия параллельных игл

4. кристаллическая форма

5. полость, содержащая пузырек газа

Negative crystal is …

Feather is …

Zircon halo is …

Two-phase inclusions are …

Three-phase inclusions are …

Inclusion silk is …
Text 2.

Clarity characteristics of diamonds

Clarity refers to the presence of internal features such as breaks or foreign bodies, called inclusions, within a diamond, and to external imperfections such as scratches (these are called blemishes). Both blemishes and especially inclusions lower the clarity grade (and the value) of a diamond, but in most cases they have very little effect on stones beauty or durability.

Many diamonds contain crystals of other minerals, called included crystals. Included crystals occur singly and in groups, and can be almost of any size. Tiny ones are called pinpoints. Groups of very tiny ones – too small to be seen individually even under high magnification – are called clouds.

Included diamond crystals that reach the stones surface are called knots. You can often see the demarcation of knot and host under magnification. Faceting may leave scratches and polish lines (groups of small parallel scratches). Diamonds inclusions distinguish it from every other diamond.

1) Both blemishes and especially inclusions lower the value of a diamond.

2) Groups of very tiny inclusions are called clouds.

3) Included diamond crystals that reach the stones surface are called knots.

1. Чистота алмаза характеризуется отсутствием внутренних включений и внешних дефектов.

2. Кристаллы включений могут быть единичными или располагаться группами.

3. Крошечные включения могут быть трудно различимы даже под увеличением.

4. Огранка может оставить на поверхности камня линии полировки.
Text 3.

“Blue” quartz

Color in most gems is caused by chromophoric elements that are either a necessary part of the gem’s chemical composition, as with peridot and turquoise, or not essential to the identity of the mineral, as with corundum and beryl. However, some gem materials gain apparent color from the presence of inclusions. Examples are the reddish orange color of some sunstone feldspars and so-called bloodshot iolite, which is attributed to the presence of ultrathin inclusions of red hematite, or the dark brown color of some star beryls and brown-to-black star sapphires, which results from numerous tiny, skeletal gray-brown ilmenite inclusions. While these inclusion-colored gems are relatively common, others, such as natural blue quartz, are much more unusual.

As thus far reported, blue color in natural quartz has always been the result of inclusions; chrysocolla, dumortierite, elbaite, lazulite have all been identified as causes of such a color appearance. Of these, dumortierite is by far the most common. Blue elbaite tourmaline, also known as indicolite, is rarely encountered, as the vast majority of tourmaline inclusions in quartz cause black to very dark brown color. Magnification revealed that the blue color came from numerous thick-to-thin, randomly scattered, euhedral fibers and rods of what appeared to be indicolite. These inclusions showed strong dichroism, from virtually colorless to dark blue (depending on the thickness of each), which was also indicative of indicolite.

Studying gems colored by inclusions is always interesting, particularly so when the inclusion-host combination is both beautiful and unusual.
Дополнительный словарь:

chromophoric – хромофорный	to attribute – приписывать
essential – существенный	ultrathin – ультратонкий
to gain – приобретать	skeletal – скелетообразный
feldspars – полевые шпаты	ilmenite – ильменит
bloodshot – «налитый кровью»	chrysocolla – хризоколла
by far – намного	dumortierite – дюмортьерит
to encounter – сталкиваться	elbaite – эльбаит
vast – огромный	lazulite – лазулит
to scatter – рассеиваться	indicolite – индиголит
randomly – беспорядочно	rod - прут, стержень

7.9. Answer the questions:

1. In what gems is colour caused by its chemical composition?

2. May the presence of foreign bodies is caused apparent color of the stone?

3. What minerals gain unusual color with internal inclusions?

4. What included minerals may be the cause of blue colour in natural quartz?

5. With what group of minerals does elbaite relate?

6. Is indicolite possessing pleochroism?
7.10. Find the following word combinations in the text:

1) хромофорные элементы;

2) полевошпатовый солнечный камень;

3) давно отмечено;

4) синий эльбаит известен как индиголит;

5) толстый до тонкого;

6) беспорядочно рассеянный;

7) зависящий от толщины стрежня.

The specimen is transparent and of gem quality, with only a few inclusions present. One side of the gem is traversed by healed fissures within which are equidimensional-to-oblong liquid or liquid-gas inclusions. Just below the surface, this healed fissure also contains a series of oblong and angular negative crystals that are associated with a series of small fissures all oriented parallel to one another. The innermost extension of the healed fissure is delineated by a long, irregular, coarsely textured etch channel that has been filled with an opaque orange-brown material. Also present are a few needle-like growth tubes and small aggregates of pinpoint inclusions.

When immersed in a near-colorless oil mixture, the poudretteite showed distinct color zoning and growth features parallel to the optic axis. An intense purple-pink color concentration was present in approximately two-thirds of the stone. No significant growth structures were visible in this highly saturated region. The boundary of this color zone was very irregular but distinct, in that it was closely paralleled by a very narrow, essentially colorless zone. The area of growth adjacent to that zone consisted of a series of planar and angular growth structures that did not repeat the irregular contour of the other two growth zones. These growth planes were oriented parallel to prism faces and consisted of alternating near-colorless and pale purple-pink bands. No twinning or other growth structures were observed.
Дополнительный словарь:

to traverse – пересекать	to etch – оставлять след
equidimensional – равномерный	tube – труба
to associate – связывать	boundary – граница
innermost – лежащий глубоко внутри	adjacent – соседний
extension – продолжение	alternating – переменный
to delineate – очерчивать, изображать

7.11. Answer the questions:

1. What structure features were seen in the specimen of poundretteite?

2. Where was the specimen immersed for the detection of colour zoning?

3. Did the sample of poudretteite contain any internal crystals?

1) немногочисленные включения;

2) залеченные трещины;

3) продолговатые жидкостные включения;

4) ориентированы параллельно друг другу;

5) иглообразные трубки роста;

The total sample set consisted of more than 1,000 sapphire crystals, about 250 faceted sapphire, and 80 star (cabochon-cut) sapphires. From this large group, we selected the samples that were tested by the various methods described below.

About 30 faceted samples were tested by standard gemological methods for optical properties, fluorescence, and density (hydrostatically). Morphological and crystallographic features of about 100 crystals were determined with a standard goniometer. The inclusion features and internal growth structures (i.e., color zoning and growth planes) of about 70 faceted and 30 rough sapphires were examined with a horizontal microscope using an immersion cell. Solid inclusions were identified by laser Raman microspectrometry with a Renishaw Raman microprobe or with a scanning electron microscope equipped with an energy-dispersive spectrometer (SEM-EDS).

Polarized ultraviolet-visible-near infrared (UV-Vis-NIR, 280 to 880 nm range) absorption spectra were recorded for 15 rough and 15 faceted natural-color sapphires (again, all colors; selected from the 100 examined microscopically above) with spectrophotometers. The orientation of the rough samples was determined in accordance with their external morphology. For the faceted sapphires, we selected only those samples with table facets that were oriented perpendicular to the c-axis, which produce the most accurate polarized spectra.

The chemical composition of 137 rough and fashioned samples, representing all color groups and the asteriated stones, was analyzed by energy-dispersive X-ray fluorescence (EDXRF) spectroscopy. These analyses were performed with Northern Spectrace – 5000 system, using a program specifically developed for trace-element geochemistry of corundum.
Дополнительный словарь:

cell – кювета, ячейка	to verify – проверять, подтверждать
in accordance with – в соответствии с	to regard – рассматривать, расценивать

8.4. Find Russian equivalent for the following words:

standard gemological methods

fluorescence

hydrostatically

goniometer

Laser Raman microspectrometry

Scanning electron microscope

Energy-dispersive spectrometer

polarized ultraviolet-visible-near infrared

spectrophotometer

energy-dispersive X-ray fluorescence (EDXRF) spectroscopy

immersion

geochemistry

microscope

1. optical properties

2. morphological features

3. absorption spectra

4. internal growth structure

5. color zoning

6. immersion cell

7. heat treatment

8. external faces
8.6. Answer the questions:

1. 
   What are standard methods of gemology?
   
2. 
   What equipment can we use to research internal structure and inclusions?
   
3. 
   What part of absorption spectra was recorded?
   
4. 
   What equipment may be used for the accurate polarized spectra?
   
5. 
   What is the result of analysis by energy-dispersive X-ray fluorescence spectroscopy?
   
6. 
   What characteristics may be tested?
   

1) огранка кабошоном;

2) звездчатые сапфиры;

3) хорошо оформленные кристаллы;

4) неровные образцы;

5) исследованы геммологическими методами;

6) микроскоп, снабженный иммерсионной кюветой;

7) ориентировка необработанных образцов.

1. 
   Морфологические и кристаллографические особенности определяются с помощью гониометра.
   
2. 
   Структурные особенности наблюдают в горизонтальном микроскопе с иммерсионной кюветой.
   
3. 
   Твердые включения идентифицируют с помощью лазерного Раман микроспектрометра.
   
4. 
   Спектрофотометр регистрирует спектры поглощения образцов.
   
5. 
   Чтобы получить точный поляризованный спектр поглощения, образец должен быть правильно ориентирован.
   
6. 
   Химический состав образцов определяют энергетически-дисперсионным рентгено-флуоресцентным анализом.
   

When classical gemological methods do not provide enough clues to solve a gem identification problem, laboratory gemologists turn to more sophisticated techniques. During the 1970s, these were UV-visible absorption spectroscopy and electron microprobe analysis. While some progress has been made in these techniques, especially microprobe analyses, other new technologies are now routinely used in some gemological laboratories.

The chemical composition of most gem materials can be determined with an electron microprobe. One of the long-standing limitations was its inability to measure the concentration of light elements, in particular oxygen. The 1980s saw the development of detection systems, such as multilayered diffraction crystals, that greatly improved the detection efficiency for light elements and therefore the accuracy of the entire analysis.

The appeal of spectroscopic methods, which involve detecting and measuring the absorption or emission of electromagnetic radiation by a material, is that they can be used nondestructively on most gems. The materials-science community adopted many techniques that had previously been used primarily in chemistry – such as infrared, X-ray, and Raman spectroscopy – to study a wider range of materials, including gems.

Infrared spectroscopy probably brought the most new solutions to gem identification problems. Originally developed by organic chemists, infrared spectroscopy was first applied to mineralogy during the 1950s. Many materials can be identified rapidly by their infrared absorption spectra. For example, turquoise can be separated from its simulants by this technique, amber can be distinguished from plastic simulants, amethyst can be separated from purple scapolite and glass can be distinguished from nonphenomenal opal. These tests are difficult, even sometimes impossible, using classical gemological techniques. In some cases, infrared spectroscopy can distinguish natural materials from synthetic ones. This is particularly important when the material contains few or no inclusions. In a number of cases, this distinction is possible because of differences in the way water is incorporated. The distinction between natural and synthetic alexandrite is based on the same principle. The fact that water was incorporated during growth in natural alexandrite results in an infrared spectrum that is different from that of most synthetic alexandrites (grown by a melt technique), which lack “water”.
Дополнительный словарь:

enough – достаточный	destructively – разрушительно
clue – ключ	community – общность
to involve – вызывать	to adopt – принимать
routinely – обычно	previously – предварительно, заранее
long-standing – давнишний	rapidly – быстро, скоро
inability – невозможность	impossible – невозможный
efficiency – эффективность	case – случай
entire – чистый, полный	to incorporate – соединять
appeal – привлекательность	to lack – нуждаться, не иметь
to sophisticate – придавать изысканность	accuracy – точность

8.9. Answer the questions:

1. What methods of the examination did gemologists used in specific laboratory?

2. What limitations had an electron microprobe?

3. Why spectroscopic methods are more applied for gemstones?

4. What materials can be identified by an infrared spectroscopy?
8.10. Complete the following sentence:

An electron microprobe analysis is used for …

An infrared spectroscopy is used for …
Text 3.

Continuation

Energy dispersive X-ray fluorescence (EDXRF) analysis is another relatively sophisticated technology that was first applied to gemology during the 1980s. In an XRF spectrometer, an X-ray beam directed at a sample causes the individual chemical elements in the sample to emit X-rays of a characteristic energy. When the instrument is carefully calibrated, the intensity of a given peak can be quantified to indicate the concentration of the corresponding element. One of the major advantages of this technique is that a cutted stone requires no sample preparation; the gem is simply placed table down in a holder above the beam.

Like infrared spectroscopy, Raman spectroscopy is a nondestructive vibrational spectroscopy that requires expensive equipment, especially if data are obtained with a Raman microprobe. In gemology it has been used to identify gemstones, to distinguish between crystalline and amorphous materials, and to separate natural stones – for example, diamond and jade – from their simulants. The most important use of Raman spectroscopy in gemology is the identification of inclusions. The Raman microprobe can focus on and identify an individual inclusion even when it is beneath the surface of a stone.

Cathodoluminescence is the emission of visible light by a material excited with an electron beam in a vacuum chamber. It does not require any sample preparation, and does not affect most common gem materials. Visual observation of the color (or distribution of color) of the emitted light is enough, for example, to distinguish clearly between natural and synthetic yellow diamonds on the basis of the distribution of their various growth sectors. Emission spectra and quantitative measurements of the emissions can also be recorded and used for some gem identification purposes, such as the separation of natural rubies, emeralds, and alexandrites from synthetic ones.

1. What another sophisticated technologies are applied to gemology?

2. What advantage has energy dispersive X-ray fluorescence analysis?

3. What is Raman spectroscopy applied for in gemology?

You will often hear the terms synthetic, simulant, imitation, substitute, and artificial in the jewelry industry. All terms apply to man-made products, but some of them include natural materials, and there are subtle but important distinctions between them. Artificial is a general term for any gem material made by man. A synthetic analog is a material, which has essentially the same chemical composition, crystal structure, optical and physical properties as the original. Synthetic rubies, sapphires, and emeralds are examples of popular synthetic gems. Synthetic industrial diamonds are manufactured for use as abrasives and cutting tools. Gem-quality synthetic diamonds are now produced commercially for scientific and industrial uses. Although they may become an important product in the jewelry industry, there is no indication that they pose a threat to the natural diamond market.

Materials, either natural or artificial, which are marketed as look-alikes for natural gems are called simulants or imitations. (Substitute is an older synonym.) Many different materials nave been used as diamond simulants: glass and zircon are classics, while YAG (yttrium-aluminum garnet), GGG (gadolinium-gallium garnet), and CZ (synthetic cubic zirconia) are modern simulants.

You need to understand these terms to answer customer’s questions and protect yourself and your store from problems and misunderstandings. During your career, you may encounter diamond simulants in repair or appraisal take-ins. Customers who have received jewelry as a gift may not know what they have, and others will try to pass off a simulant as a diamond – and then accuse you of switching stones. To avoid problems, many professionals describe stones on take-in forms as accurately as they can in a flexible, noncommittal way, without recording anything that is not certain. They might, for example, describe what appears to be a diamond solitaire as: “Woman’s ring set with one near-colorless brilliant, stated by customer to be diamond.”

1. synthetic industrial diamond

2. older synonym

3. yttrium-aluminum garnet

4. gadolinium-gallium garnet

5. broken bipyramidal crystal

6. manufactured material

7. synthetic cubic zirconia

8. noncommittal way
9.4. Answer the questions:

1. How the natural stones and many artificial materials difference?

2. Can professional gemologist distinguish any simulant of gemstone?

3. Has synthetic material the same chemical composition as the original?

4. Where are synthetic industrial diamonds used?

5. May gemologist make any mistake in appraisal of jewelry?

1. Твердые синтетические материалы используют как абразивы или режущие инструменты.

2. Заменитель является устаревшим термином.

3. Стекло и циркон, ИАГ и фианит являются современными имитациями алмазов.

4. В течение своей работы вы можете обнаружить в ювелирных изделиях подмененные камни.
9.6. Complete the following sentence:

Synthetic materials are…

Artificial is…

Simulants are called…