New and Unusual Cat’s Eyes and Asteriated Gems

Martin P. Steinbach, Lore Kiefert, Jeanette Fiedler

(1.STEINBACH-Gems with a Star, Idar-Oberstein 55743, Germany;2.Dr. Lore Kiefert Gemmology Consulting, Heidelberg 69115, Germany;3.DDI-Foundation German Diamond Institute, Pforzheim 75172, Germany)

Abstract： The article describes 6 types of gemstones which show phenomena such as chatoyancy and asterism. The gemstones have not been described before, either because they come from new sources, or because the phenomenon has not been seen before in the type of gemstone described. Gems from the new sources are star garnet from the Karelia Province in Russia, and star garnet from the Jiangsu Province in China. Grandidierite usually does not show a cat’s eye effect, but the two described samples display a weak cat’s eye. An unusual white quartz from Brazil with a sharp cat’s eye is described, as well as a star sapphire with two differently coloured stars on each side of the cabochon, as well as a trapiche-type quartz. The stones were tested with gemmological, microscopic, and advanced techniques and the results are presented.

Key words: cat’s eye; star; asterism; chatoyancy; quartz; grandidierite; sapphire; garnet

INTRODUCTION

Gems that show a star effect (asterism) or a cat’s-eye (chatoyancy) effect are known since antiquity.Dionysius Periegetes, who lived in the first century AD, wrote a description of the ancient world in Greek. He was the first who mentioned a “beautiful stone asterios” from the Pallenes Mountains in Thracia (Greece). Pliny the Elder (23 A.D.-79 A.D.), was a Roman author, philosopher, scientist, and army commander. With his monumental masterpieceHistoria Naturalis(circa 77 A.D.-79 A.D.), he influenced the thinking about star stones well into modern times. In book 37 of hisHistoria Naturalis, Pliny described at least 4 varieties of stones with light phenomena: Asteria, Astrion, Astriotes and Astrobolos.

Asterism is generally caused by oriented acicular crystals, often rutile. The needles are oriented to create 4, 6, 8 or even more rays due to the fact that they are exsolutions within the host crystal and follow its crystallography. The cat’s eye effect is frequently formed by fibrous parallel inclusions that run only in one direction. Occasionally, parallel hollow tubes or a set of parallel fissures can also create chatoyancy.These optical phenomena are best seen with a spotlight or better, the sun. Stars are seen in epiasterism (reflected) and diasterism (transmitted) light.

Star stones that are best known and highly appreciated are blue star sapphires as well as star rubies. The most important countries of origin of asteriated gems are Brazil, India, Myanmar, Thailand and especially Sri Lanka, the “island of gems”, which is also known for the classical cat’s eye, the chrysoberyl cat’s eye.

Beside the well-known star ruby and star sapphire, over 40 different gemstones display a star, and more than 200 gem varieties are known to show a cat’s eye effect. Trapiche gems possess a fixed, not movable star, which is caused by a different material separating mostly hexagonal sectors from each other. The most famous trapiche gemstones are emeralds. They receive more and more attention, and since a short time, also trapiche-like star gems appear occasionally. These have a similar fixed pattern like trapiche gems but are not separated by a different material.

Occasionally, stars and cat’s eyes occur in gems that are not known for this effect. One such example is tourmaline. While tourmaline cat’s eyes occur in all colours and sizes and are well known and highly appreciated, star tourmalines are practically non-existing.

Like all gemstones, stars and cat’s eyes can be manipulated and enhanced; also synthetic stars and cat’s eyes are known. This article describes some less known untreated star and cat’s eye gem varieties, and a so-called trapiche-like star gem.

FAMOUS GEMS WITH PHENOMENA

The most famous cat’s eye gem is the “Maharani Cat’s Eye” (chrysoberyl) in the Smithsonian Museum of Natural History in Washington, D.C. With its exceptional size of 58.19 ct, honey colour, and sharp band of light, and this gem from Sri Lanka is one of the finest of its kind.

The possibly most famous star ruby is the “Rosser Reeves (Star) Ruby”, which also traces its origin to Sri Lanka. The ruby is noted for its prominent star pattern and attractive colour. The ruby was donated to the Smithsonian Museum of Natural History in Washington, D.C. in 1965 by Rosser Reeves, an advertising mogul, after whom the gemstone is named. The ruby weighs 138.70 ct.

Another famous star ruby is the “DeLong Star Ruby”. Named after its owner, Edith Haggin DeLong, this precious gemstone was uncovered in Myanmar in the 1930s. The gemstone weighs 100.32 ct. In 1937, the owner of the gemstone donated it to the American Museum of Natural History in New York City (AMNH). This gemstone was one of the precious gems that were stolen during a notorious heist conducted by JR Murphy and his accomplices in 1964. Although some of the other gemstones stolen during this robbery were recovered, a massive ransom amount had to be paid to get back the DeLong Star Ruby. The amount was paid by a wealthy businessman from Florida.

Two famous star sapphires are the blue “Star of India” and the black “Star of Queensland”.The “Star of India” is a 563.35 ct star sapphire, one of the largest of fine quality in the world, and the fact that it has stars on both sides of the stone is unusual. The greyish-blue gem was mined in Sri Lanka and is on display in the American Museum of Natural History in New York City (AMNH). The “Star of Queensland”, named after its nature and place of origin, is a 733 ct black sapphire, and was the world’s largest gem quality star sapphire for a long time(Steinbach, 2016).

MATERIALS AND METHODS

This article describes two varieties of cat’s eyes: 2 pieces of grandidierite cat’s eyes and 2 pieces of white, unusual quartz cat’s eyes. 3 pieces of different stars gems from either new locations or with a special effect are described: 2 pieces of star garnets, 2 pieces of star rose quartzes, and a rare star sapphire with a white and a golden star on the two different sides of the cabochon. In addition, a new type of trapiche-like star quartz is described. All stones were acquired by Martin P. Steinbach.

As far as possible due to size and the type of cut, gemmological data such as refractive index, behaviour in the polariscope, and dichroism were taken, as well as microscopic observations. All gems except for the 2 pieces of big spheres were analyzed with a GemmoRaman for their authenticity. In addition, the 2 pieces of white quartz cat’s eyes were analysed with a GemmoFTIR for authenticity, and the grandidierite cat’s eyes for any clarity enhancement also with FTIR. All tests were performed at the DDI Foundation German Diamond Institute by Lore Kiefert and Jeanette Fiedler.

GrandidieritewithACat’sEyeEffect

Grandidierite is a relatively new gem material. The first gem-quality sample from the Kolonne area in Sri Lanka was described in 2003 (Schmetzer et al., 2003), and grandidierite from Madagascar was only found in 2015 (Vertriest et al., 2015; Bruyre et al., 2016). In 2019, two grandidierites with a weak cat’s eye effect were acquired from a Madagascan gemstone dealer at the St. Marie-Aux-Mines mineral fair. The gems are supposed to come from Tranomaro in S.E. Madagascar. Cat’s eye effects have not been encountered before in grandidierite.

One cabochon measures 14.36×10.42×7.06 mm and weighs 8.48 ct. It is translucent and its colour is greenish-blue to blue-green. An RI spot reading gave a value of approximatelyn=1.58, in the polariscope a clear but weak double refraction was visible. The pleochroism changed from blue-green to colourless in one direction and from blue-green to green in the other direction.Microscopic observations revealed a dense network of parallel fissures mainly in one direction across the stone, with a second set at an angle to each other, some with whitish debris. These fissures cause the cat’s eye effect. Between the fissures short reflective needles and particles can be seen along the length of the stone which may be responsible for a very weak star effect, seen from the side.

The second grandidierite cat’s eye measures 10.28×7.30×4.29 mm and weighs 2.60 ct (Fig.1a). The colour is also greenish-blue to blue-green, and it is also translucent. A better RI reading on this sample showed a value ofn= 1.58 and 1.60, which is in agreement for values of grandidierite. In the polariscope, the stone appeared light, with no extinction seen. Pleochroism was the same as in the larger sample.Microscopically, the stone showed similar inclusions to the larger grandidierite. A distinct system of partly very fine parallel fissures across the stone is responsible for the cat’s eye effect. Perpendicular to this system was another, less dense system of fissures in a ninety degree angle. Between the fissures, short reflective needles and particles were observed (Fig.1b). Few small transparent colourless crystals were observed but could not be identified.

Both gemstones were positively identified as grandidierite with Raman spectroscopy (Fig.1c), and FTIR showed no signs of oiling or other treatment of the fissures (Fig.1d).

Fig.1 (a) Grandidierite cat’s eye weighing 2.60 ct. The cat’s eye is clearly visible along the stone;(b) Microscopic image of the 2.60 ct grandidierite, showing the fissures responsible for the cat’s eye effect. Field of view: 1.50 mm; (c) Raman spectra of the 8.48 ct grandidierite. A comparison with reference spectra gives a very good match;(d) FTIR spectra of the two grandidierites.The area between 2 800 cm-1and 3 100 cm-1 shows no signs of a clarity enhancement. The strong peak between 2 300 cm-1 and 2 400 cm-1 is an artefact from ambient CO2.

White Cat’s Eye Quartz from Brazil

Only few publications exist about cat’s eye effects in quartz (Welch, 1987; Koivula, 1987), and it is mostly mentioned in connection with other phenomenal quartzes. Cat’s eye quartz has been mentioned from Brazil (Koivula, 1987), Sri Lanka, and Bavaria (Manutchehr-Danai, 2009).

Two remarkably translucent pure white samples from Brazil with a strong eye were acquired at the Tucson fairs in 2016. The samples weighed 17.19 ct and 12.22 ct, and measured 16.00-16.08× 9.28 mm and 13.99-14.14×8.66 mm. Both samples were cut as round cabochons (Fig.2a). Refractometer spot reading gave an RI of 1.53 for both, and both stayed light on the polariscope, indicating an aggregate (Fig.2b). Both stones showed fine parallel white fibrous inclusions which are responsible for the cat’s eye effect (Fig.2c). Both also showed a second set of fibres from the back side, which caused a second, weaker ray. Only in one sample very few healed fissures could be observed. Although the nature of the fibres could not be determined, it is likely that they are either rutile, sillimanite, or dumortierite, as they have been observed in other star and cat’s eye quartzes (Kiefert, 2003; Woensdregt et al., 1980; Applin & Hicks, 1987).

Fig.2 (a) White quartz cat’s eyes from Brazil; (b) Polariscope image of two white cat’s eye quartzes, one grandidierite (blue), and one trapiche-type quartz. All stones did not show any extinction, indicating an aggregate rather than single crystals;(c) Fibrous inclusions form the cat’s eye perpendicular to the direction of the fibres; (d) Raman spectra of white quartz from Brazil.

Raman spectrometry confirmed the stones to be quartz (Fig.2d), despite its aggregate-like character observed in the polariscope. FTIR spectrometry gave a clear 3 594 cm-1absorption band, a sign that the stones are natural.

Star Garnets from A New Source in Russia

Star garnets are well known for a long time and are described extensively in the literature (Eppler, 1958; Welch, 1988; Koivula, 1989; Kumaratilake, 1998; Schmetzer et al., 2002; Steinbach, 2011, 2016). Star garnets occur in nearly all garnet species and varieties, however, they are most frequently encountered in pyrope-almandine. Stars in colour-change varieties are also reported (Steinbach, 2016). Star garnets are also found in many countries, the major ones being Brazil, India, Kenya, Madagascar, Sri Lanka, Tanzania, USA and Vietnam for the pyrope-almandine varieties, Brazil and Sri Lanka for star spessartine, and Japan, Mexico and USA for star andradite (Steinbach, 2016).

2 pieces of star garnets were acquired at the Tucson fairs in 2014 from a Russian gemstone dealer (Fig.3a and Fig.3b). Both stones are reportedly coming from the village Shureretskoe in Russia’s Karelia Province (Steinbach, in preparation). The first garnet is a sphere of a diameter of 60 mm and a weight of 531.71 ct in a dark reddish-brown colour. The second one is a relatively flat cabochon measuring 50.30×40.36×9.33 mm, weighing 225.01 ct in the same colour. Both garnets are opaque to the naked eye and belong to the pyrope-almandine series.Due to its large size, it was not possible to take any gemmological data of the sphere. The cabochon gave an RI that was over the detection limit, and in the polariscope it showed a distinct anomalous double refringence.

Both stars are caused by whitish reflecting needles in two directions, possibly rutile, in an angle of approximately 60° to each other. In the sphere, a third direction is marked by lines of particles (dust tracks). Dark irregular needles that appear black are interspersed between the whitish needles and the dust tracks, which appear like hematite needles in black star sapphires. The cabochon shows, besides the whitish reflecting needles forming the star, wavy dust lines as well as black irregular flakes (Fig.3c).

In addition, black-opaque large to light reddish-brown small, mostly prismatic minerals were observed in the sphere, similar to rutile crystals in corundum. Long green fibrous to rod-like minerals could be observed, possibly pyroxene, as well as transparent colourless rounded to isometric grains, possibly quartz grains. A larger grey-metallic sphere was cut on the surface, probably pyrite. The cabochon contained rounded to isometric colourless crystals with a soft relief. Fissures in the stone were filled with a soft dark material. Raman spectra taken on the cabochon at four different places all gave a good match with pyrope-almandine (Fig.3d).

Fig.3 (a) Large garnet sphere of 531.71 ct showing a four-rayed star;(b) Star garnet cabochon of 225.01 ct showing a four-rayed star;(c) Microscopic image of the star garnet cabochon showing wavy dust lines and irregular black flakes. Field of view: 2.5 mm; (d) Raman spectra of the star garnet cabochon. A comparison with reference spectra gives a good match.

Star Rose Quartz from A New Source in China

Asteriated rose quartz has been known from various localities for more than a century, and the material is seen occasionally in the trade, with most samples originating from Brazil or Madagascar (Cassedanne & Roditi, 1991; Pezzotta, 2001). Most common are asteriated stones presenting six-rayed stars, with three groups of needle-like inclusions oriented in a plane perpendicular to thec-axis. Occasionally, twelve-rayed stars are observed, which show six groups of needles (two sets of three) in the same plane (Schmetzer et al., 2015; Steinbach, 2016).

At the 2015 Tucson show, two star rose quartzes were selected from a large lot of rose quartz spheres. The stones were mined in the Donghai city area in Jiangsu Province, China (Steinbach, in preparation). The first sphere has a diameter of 41 mm and weighs 515.45 ct, the diameter of the second sphere has a diameter of 32 mm and weighs 258.93 ct (Fig.4a and Fig.4b). Both spheres are light pink and transparent to translucent.The larger rose quartz sphere showed a spot reading ofn=1.54, the smaller one gave a value of 1.53. Both were doubly refractive, and in the smaller sphere, a clear bull’s eye was visible.

Both spheres showed large reflective fissures, partly with a whitish substance, and healed fissures. The star is caused by very fine, sub-microscopic particles, which occasionally appear denser and as grey shadows or bands. Besides these, the larger sphere showed one long reflective needle (Fig.4c), while the smaller sphere contained some pseudo hexagonal quartz crystals in a different orientation than the host.

For both stones, an FTIR spectrum was not possible to take, and only one Raman spectrum could be taken on the smaller sphere, which confirmed the stones to be quartz (Fig.4d). Based on the inclusions, a natural origin could be confirmed.

Fig.4 (a) Star rose quartz sphere of 515.45 ct;(b) Star rose quartz sphere of 258.93 ct; (c) Long isolated needle in the larger star rose quartz, marked with an arrow. Field of view: 3.8 mm; (d) Raman spectra of the smaller star rose quartz. An artefact of the chalcedony absorption band at around 500 cm-1 is barely visible.

Black Star Sapphire with A White and An Additional Golden Star

As mentioned in the introduction, star sapphire and star ruby are the best known and most popular asteriated gems. They have been described in many articles and books (Gübelin & Koivula, 1986; Hughes, 1997; Steinbach, 2016; Hughes et al., 2017). Star sapphires occur in many colours and hues, among them there are famous black star sapphires such as the “Black Star of Queensland” or the “Star of Jolie”, a 888.88 ct pear-shaped star sapphire in a necklace (Steinbach, 2016), also from Queensland, Australia. Black star sapphires occur in many countries of the world together with precious sapphire, but most pieces come from Australia or Thailand. Generally, these stones occur in a dark, nearly black colour, but occasionally they can also appear golden such as some rare golden star sapphires from Chanthaburi (Steinbach, 2016) or a recent find from Kenya (Narudeesombat et al., 2016).

An unusual black star sapphire was acquired in Chanthaburi in Thailand in 2014 and was mined in the gem fields surrounding this city (Steinbach, in press). It is an oval double cabochon, which weighs 3.03 ct and measures 10.75×8.88×2.85 mm (Fig.5a).The cabochon showed a golden and a black side, with a white star on the black side as is found in many black star sapphires, but on the golden side a golden star was visible, which reminded of the stars found in star sapphire from Kenya (Fig.5b and Fig.5c). A similar star sapphire was described by Koivula and Tannous (2001). A thin black line was separating the two different stars along the girdle, so that it appeared to be a doublet (Fig.5d).

Fig.5 (a) Black star sapphire double cabochon with a black side (top) and a golden side (bottom); (b) White star on the black side of the double cabochon;(c) Golden star on the golden side of the double cabochon; (d) At one side of the double cabochon an irregular large fissure was present along the girdle, marked with an arrow; (e) Dense short needles on the black side of the double cabochon forming a star. Field of view: 1.2 mm; (f) Short needles arranged in a trigonal pattern. Field of view: 2.0 mm.

However, microscopic observations revealed that the black line was an irregular fissure with a whitish substance along part of the girdle along half of the stone. On one side of the large fissure, the needles are a dense network of very short reflective rutile needles in three directions, forming the white star on the side appearing black (Fig.5e). On the other side, the needles are arranged in a less dense concentration around a trigonal core, so the stone appears golden (Fig.5f). Raman spectroscopy confirmed the stone to be corundum, treatments were not observed.

QuartzwithAnUnusualTrapiche-likeStar

Trapiche and trapiche-like gemstones have received more and more attention in recent years (Steinbach, 2016). The term “trapiche” is linked to its specific growth pattern which is often compared to the spikes of a wheel. Such gemstone consists of segments that are separated by fine flakes of a different material than the host. The best known are trapiche emeralds, which have already been described extensively at the beginning of the 20thcentury (Bernauer, 1926), and in gemmological text books. Since the end of the 20thcentury, many more trapiche gemstones as well as trapiche-types have appeared on the market such as trapiche rubies (Schmetzer et al., 1996), trapiche tourmaline (Hainschwang et al., 2007) or trapiche-type sapphire (Kiefert, 2012).

An unusual trapiche-type quartz which originated from Inner Mongolia was acquired at the St. Marie-Aux-Mines mineral show in France in 2019 (Farfan et al., 2021; Liu & Wathanakul, 2021). This flat cabochon weighs 12.21 ct and measures 17.76-18.05×4.80 mm. The body colour is a translucent white with light brown more opaque segments (Fig.6a). In the polariscope, the stone stayed light like an aggregate (Fig.2b), and a spot reading on the refractometer gave a refractive index of 1.54.Microscopically, the more transparent whitish area was marked by sub-microscopic fine particles giving the stone a milky sheen. Interspersed were few black short-prismatic minerals and very few flake-like particles.The brown areas were dominated by reflective particles and brown irregular flakes described as protogenetic clay inclusions by Farfan et al. (2021).

Raman spectroscopy gave a clear quartz signal without any additional peak (Fig.6b), confirming this gem to be a single-crystal quartz rather than chalcedony, despite the unusual polarizing behaviour.

Fig.6 (a) Trapiche-type quartz with brownish segments made of fine particles; (b) Raman spectra of the white (red line) and brown (blue line) sections of the trapiche-type quartz. A good match with the reference spectrum was found (black line).

CONCLUSIONS

The above examples have shown that new gemstones are constantly being found, be it as new varieties or known varieties from the new sources. The cat’s eyes described above are examples of new varieties of a known stone, and the star garnets and star rose quartzes are examples of known effects, but in new locations besides the already known ones for this type of gem. In addition, the black star sapphire with two differently appearing sides, or the trapiche-type quartz with its brown segments, are examples of unusual phenomena in known stones. The examples also show that the stars are formed by very fine inclusions which often cannot be identified properly, such as the fine submicroscopic particles and fibres in the rose quartz.