Posts by Lareef

Thanks Lizc for the trust placed on our forums. The thread on Alexandrites started on May 21st 2014 by Gemlite generated an extensive discussion, citing alexandrites of different countries of origin that appeared at public auctions conducted by Christie's and Sotheby's over the years, and went on till around the end of August 2014. The discussion brought out the salient features of Alexandrites from source countries such as Russia, Sri Lanka and Brazil and also established a market ranking for alexandrites based on country-of-origin, which goes as :- Russia - Brazil - Sri Lanka - Others. According to this discussion the average price-per-carat value of Russian alexandrites vary between US$50,000-US$70,000. The PPC values of Brazilian alexandrites vary between US$20,000-US$50,000 and those of Sri Lanka alexandrites between US$5,000-US$20,000.

It is highly unlikely that your gemstone is a color-change diaspore or a color-change fluorite. Color-change diaspores are a recent discovery from Turkey in the 1990s, but the ring incorporating your color-change gemstone had existed in your family in the late 60s or early 70s. Color-change fluorites have a low hardness on the mohs scale and good cleavage properties and hence their use in jewelry is limited. If at all they are used in jewelry they can be set only on pendants and earrings, which are not subjected to wear and tear like rings and bracelets. Your piece of jewelry is a ring, and hence it is unlikely that the stone set in the ring is a soft fluorite.

We are now left with three options - alexandrite, color-change sapphire and color-change garnet, whose hardness is respectively 8.5, 9.0, and 6.5-7.5 on the mohs scale, and all of which are used on ring settings. According to you the color change in your gemstone is from a teal blue color in natural daylight to a purple color in indoor lighting. I hope by indoor lighting you mean incandescent lighting and not fluorescent lighting. I have also noticed a brown color associated with the purple color in image 3 you have uploaded. If this is a true brown color associated with the stone in incandescent lighting and not a reflection of its background, the color of the stone in incandescent lighting can best be described as brownish-purple.
Blue to Purple color change from natural daylight to incandescent light are found in some alexandrites originating from Brazil; rare variety of color-change sapphires and color-change garnets from some countries. Pyrope-spessartite color-change garnet found in the Umba Valley of East Africa change color from greenish-blue in daylight to reddish-purple in incandescent light. Color-change garnets from Bekily, Southern Madagascar change color from blue in natural daylight/fluorescent light to red/purple in incandescent light. Sri Lanka color change garnets change color from blue/green/gray in natural daylight to reddish-purple in incandescent light. Out of the three color-change gemstones - alexandrite, sapphire and garnets - the rarest is the color-change sapphire. The occurrence of alexandrites and color-change garnets are also rare but not so rare as color-change sapphires. Hence, your gemstone Lizc is most probably an alexandrite or color-change garnet and not an extremely rare color-change sapphire. If the gemstone is an alexandrite, based on the color change you have observed (blue to purple), the alexandrite is probably of Brazilian origin, but not from Hematita mine where alexandrites were discovered only in 1987. If there is a tinge of brown in the colors you have observed the alexandrite is most probably of Sri Lankan origin. If the gemstone is a color-change garnet, it can be either from the Umba Valley where gemstone deposits were discovered in the mid 1960s or Sri Lanka the oldest source of gemstones of several varieties including garnets. It cannot be a Bekily color-change garnet where such stones were exploited only in the late 1990s.

Welcome to our forums Asiboy ! Thanks for highlighting the discovery of a fossilized Giant Clam Shell high up in the mountains of San Fernando in the island province of Cebu in the Philippines. Your attempt to explain the presence of the fossilized giant clam shell in the mountains of San Fernando in an article published in your blog, philippineblog.com is very much appreciated, and contains a wealth of information about the geography and geology of the Philippines and the biology and ecology of the Giant Clam, Tridacna gigas, whose natural home are the coral reefs in the waters of the South China Sea surrounding the Philippines and also the Great Barrier Reef in the waters of the Pacific off the coast of Queensland in northeast Australia.

The Philippine archipelago of over 7,000 islands is situated at the convergent boundary of two major tectonic plates, the Eurasian Plate and the Philippine Sea Plate. When the plates collide and one subducts, the geological events that follow are the formation of trenches, volcanic activity leading to the formation of volcanic mountains and the thrusting and folding (Orogenesis) of plates to form fold mountains. Though most of the mountains in the Philippines appear to be of volcanic origin, the mountains of the Cebu Island and particuarly the San Fernando mountains appear to be of Orogenic origin, formed by the thrusting and folding of convergent tectonic plates. During this process areas that were previously under the ocean would have been raised up to form mountains.This explains how the Giant Clam reached the mountain tops of San Fernando in the Island of Cebu, where its fossilized remains were discovered. The extensive limestone deposits in Cebu also seems to be related to the Orogenic activity that brought up these deposits formed in the ocean bed as sedimentary rocks by the accumulation of dead corals, shells of dead mollusks, and foraminifera. The limestone deposits of the Mananga Group of rock formations date back from the Cretaceous to Paleocene age, 145 million to 60 million years ago.Sedimentary limestone deposits of the Lutak Hill Formation, Cebu Formation and Malubog Formation date back from the late Eocene to Early Miocene periods, 38 million to 23 million years ago. The Luka Formation and the Uling Limestone Formation are middle Miocene rock formations dating back to around 15 million years ago. The conglomeratic limestone deposits of the Maingit Formation belong to the late Miocene period and are around 7-15 million years old. Hence, most of the hard limestone deposits in the Cebu Island are between 7-145 million years old. Limestone deposits more recent than this are coralline, porus and soft, poorly bedded and sandy.

The convergent tectonics that led to the orogenesis of the San Fernando mountains could have occurred any time between the Upper Cretaceous (70-100 million years ago) and Pleistocene (0.1-2.5 million year ago), the period during which complex tectonic processes were intermittently active. Hence, the period during which the orogenesis of San Fernando mountains took place can be estimated only if the age of the limestone deposits in these mountains are determined. If for instance, the age of the limestone deposits are found to be around 15 million years old, the orogeneisis of the mountains must have taken place after this, ie. anytime between 15 million and 0.1 million years ago.

However, it is important to note that the geology of the Philippines is more complex than the effects of just a convergent boundary between the Philippine Sea Plate and the Eurasian Plate. In fact in the tectonic boundary between the Eurasian Plate and the Philippine Sea Plate a complex zone exists known as the Philippine Mobile Belt, upon which most of the islands of the Philippine archipelago are situated. An interesting feature observed here is that both the Philippine Sea Plate to the East and the Sunda Plate (Extension of the Eurasian Plate) to the west, undergo subduction beneath the Philippine Mobile Belt, forming two subduction zones, the Philippine Trench to the east and the Manilla Trench to the west.The Philippine Mobile Belt situated between the two trenches is composed of a number of crustal blocks or microplates, which have been sheared off the adjoining major plates. The crustal blocks or microplates are strips running in the north-south direction and the boundaries or zones of convergence between them are the fault lines of the Philippines Fault System. It is the convergent tectonic forces generated by the two subduction zones situated east and west, responsible for compressing the tectonic plates of the Philippine Mobile Belt, lifting parts of the Philippines and causing extensive faulting, mainly in a north-south direction, and it is the same tectonic forces responsible for the earthquakes and volcanic activity of the Philippines.

As in the Christie's "Jewels : The London Sale" held on June 10, 2009 highlighted previously by AnitaP, signed pieces by reputed jewelry designers and jewelry houses, had also performed extremely well at the May 13, 2009 Christie's Jewels : The Geneva Sale, registering prices much above the upper estimate. This was clearly evident in the three lots 114, 117 and 120 highlighted by shah, all exceptional pieces designed by reputed jewelry house, Van Cleef & Arpels.

Lot 114, sold for US$65,968 which was 2.9 times the lower estimate of US$22,632 and 2.4 times the upper estimate of US$27,158. Lot 117 sold for US$111,918 which was 2.5 times the lower estimate of US$45,264 and 1.5 times the upper estimate of US$72,422. Lot 120 sold for US$133,756 which was 1.6 times the lower estimate of US$81,475 and 1.2 times the upper estimate of US$108,633. Apart from the unique design features that contributed to the escalation of price realized, the other contributory factor appears to be the use of diamonds and expensive colored gemstones like rubies and sapphires in the settings.

The other signed pieces that performed well at these auctions, are Lot 24 and Lot 107. Lot 24 was An Agate Cat Figure - by Faberge and Lot 107 - An Ebony, Sapphire And Diamond "Blackamoor" Brooch, by Codagnato. Antique pieces by Faberge always fetch premium prices at public auctions and Lot 24 was not an exception. The lot sold for US$34,121 which was 7.5 times the lower estimate of US$4,526 and 5.4 times the upper estimate of US$6,337. Hence in terms of escalation of estimated price Faberge's piece had out performed all other seven animal and plant motif lots at this auction.

Lot 107 - An Ebony, Sapphire and Diamond "Blackamoor" Brooch by Codagnato sold for US$18,198 which was twice the lower estimate of US$9,053 and 1.3 times the upper estimate of US$13,579. The brooch was designed by Attilio Codagnato, a world renowned jewelry artisan from Venice, Italy, the current owner and 4th-generation heir of Casa Codagnato founded in 1866, by Attilio's great-grandfather, Simeone Codognato. Attilio's work continues with the family tradition of exquisite jewelry making using the finest materials. The prized Codognato blackamoor designs are inspired by the paintings of 15th century Venetian artist Vittore Carpaccio and 18th century painter Pietro Longhi.

Codognato "Blackamoor" brooches are as popular and highly collectible as Nardi's blackamoor brooches, first designed and popularized by Nardi, the renowned Venetian jewelry designer based on the famous Venetian Icon, the Moretto depicting the head and shoulders of a turbaned Moor of Venice, with its gem-encrusted turban and tunic. Nardi's blackamoors became very popular in the 1920s and 1930s.

The four factors highlighted above for the Christie's "Jewels : The London Sale," held on June 10, 2009, that had a bearing on the prices achieved, also applies equally well for the lots highlighted by Peter that appeared at Christie's Jewels : The Hong Kong Sale held on May 26, 2009.

Factor 1 - Signed pieces from reputed designers and jewelry houses - had a bearing on the price achieved by Lot 1505, a signed piece by Van Cleef & Arpels, assigned a higher pre-sale estimate of US $23,330 - $36,292 and selling within this estimate for US$32,404.

Factor 3 - Lots set predominantly with diamonds - had a bearing on the price achieved by Lot 1670, the teddy bear pendant, set entirely with colored diamonds. The lot sold for US$35,644 above the estimated range of US$20,738 - 32,403.

However, Lot 1509 - A Chalcedony, Ruby and Diamond Clip Brooch - even though a signed piece by Van Cleef & Arpels, was assigned a relatively low estimate of US$3,111 - $4,536 and was sold at the upper estimated value of US$4,536. The probable reasons for the lower estimate and the relatively low price achieved despite being a signed jewel by a reputed jewelry house are :-

1) The piece being made mainly of textured 18k gold.
2) The limited quantities of colored gemstones used on the piece, the main colored gemstone being a relatively cheap oval-shaped green chalcedony known as chrysoprase.
3) The five brilliant-cut diamonds surrounding the eye are the most expensive gemstones used on the piece.

Thanks AnitaP for your post. Some significant facts emerge from your post. The 7 lots highlighted by you appeared at the same auctions and hence are suitable for a comparative analysis. An analysis of the prices achieved clearly reveal the following :-

1) Signed pieces from reputed designers and jewelry houses performed exceptionally well at the auctions registering prices several folds above the upper estimate.
Lot 8 designed by Van Cleef & Arpels sold for US$16,350 which was 3.4 times the lower estimate and 2.5 times the upper estimate.
Lot 51, also designed by Van Cleef & Arpels sold for US$9,810, which was 3.4 times the lower estimate and 2.4 times the upper estimate.
Lot 62, designed by Cartier sold for US$8,584, which was 3.5 times the lower estimate and 2.7 times the upper estimate.
Lot 79 designed by Charlton sold for US$26,569, which was 3.3 times the lower estimate and 2.0 times the upper estimate.

2) Antique pieces were not only assigned a higher pre-sale estimate but also registered a price either within this estimate or slightly higher than the upper estimate.
Lot 33, designed around year 1930 during the Art Deco period, was not only assigned a higher estimate of US$9,696 - $12,928 but also registered a price within this estimate of US$12,263.
Lot 119, an Art Nouveau dragonfly brooch was also assigned a higher estimate of US$19,392 - $24,240 and registered a price slightly higher than the upper estimate of US$24,525.
Lot 165, a pair of Art Deco bird brooches was assigned a pre-sale estimate of US$8,080 - $12,928 and registered a price slightly higher than the upper estimate of US$13,898.

3) Lots set predominantly with diamonds, lots 33, 119 and 165 were assigned a higher estimate as expected and also sold within the estimate or slightly above the upper estimate.

4) The most significant escalation in price was seen in Lot 79, which sold for the highest price of US$26,569, a signed piece predominantly made up of diamonds and assigned a higher estimate of US$8,080 - $12,928. In this case it appears that factors 1 and 3 above had a bearing on the escalation of the estimated price, viz. the fact that the piece is a signed jewel by Charlton and the fact that the piece is predominantly set with diamonds.

The answer to your question Joan seems to be inherent in the wording of your question. The main reason for the exceptional showing of this lot appears to be its antique origin dating back to the early 18th-century. The use of ivory and natural pearls in the brooch, materials to which a premium value is attached is another reason for the exceptional performance of the lot, realizing over USD 7,000 when compared to the other four brooches which registered an average price of around USD 1,000.

The quality of his jewelry using a combination of colored gemstones and diamonds, with an almost invisible pavé-setting, mounted on a dark metal alloy, highlighting the color of the gems, and the use of plant and animal motifs is undoubtedly the primary reason for the popular demand for his jewelry. This fact combined with the designers unconventional methods, such as his scorn for modern marketing techniques, had served to enhance the demand for his jewelry.

The cult-like following enjoyed by the designer combined with the limited production and unconventional methods had served to increase the demand for JAR's jewelry to unprecedented levels, making such jewels the most sought-after at public auctions. This explains the highest price recorded by the Pair of Diamond and Black Diamond Hedgehog Ear Clips designed by JAR out of the six plant and animal motif lots that appeared at the Christie's New York Rockefeller Plaza, Jewels : The New York Sale held on April 22, 2009. The staggering US$1,181,346 recorded by a JAR jewel highlighted by sunil above, designed in 1989 as three stylized leaves pavé-set with emeralds, peridots, garnets, citrines and zircons at a Christie's auction in Geneva on November 12, 2013, serves to further strengthen this fact.

It is highly unlikely Jack. As Peter has already pointed out, Schlumberger was held in high esteem by Tiffany's that he was among the few designers employed by the company, who were given the freedom to sign their own work. Lot 7 was just signed as Tiffany & Co. which necessarily means the anonymous designer of this piece was not granted the same privilege as Schlumberger.

Thanks pegdenirp for your query, seeking information on the 990.25-carat Paola Emerald rough believed to be in the custody of the HK Bank. Unfortunately, there is not much information on the web concerning this enormous emerald, such as the country of origin, the mine of origin, the date of discovery, the company or individual involved in its discovery, the possible reasons why the emerald was named the Paola Emerald etc. Even an image of the rough emerald is not available on the net. Such information is important if we are to create a dedicated page for this emerald, significant in terms of its size and possibly other value factors.
We are indeed prepared to create a dedicated page for this emerald if and when sufficient information becomes available. If you have any information regarding this important emerald, please be free to upload such information to our forums or send it to our e-mail address.
Visitors to our forums who might have more information on this emerald, are also invited to provide such information as prescribed above.

Rubies and sapphires belong to the same group of minerals called corundum, which is a crystalline form of aluminum oxide. The red color of rubies is caused by chromium atoms which displace some of the aluminum atoms in the crystal structure of aluminum oxide. These chromium atoms that impart color to the rubies also interfere with the growth of the crystal leading to the formation of cracks and fissures in the crystal. Thus the ruby crystal can only grow to a limited size without flaws in the crystal. This explains why most of the high quality rubies with the minimum of flaws are mostly less than 100 carats in weight. High quality rubies greater than 100 carats in weight are extremely rare. Enormous rough ruby crystals weighing thousands of carats do sometimes occur in nature. However, such crystals are not of gem-quality and contain lots of cracks and fissures. The single large crystal of ruby used to carve out the pineapple in Schlumberger's brooch appears to be such a large non-gem quality naturally occurring ruby crystal.

Demantoid is the green variety of Andradite Garnet. Andradite is Calcium Iron Silicate with formula Ca3Fe2(SiO4)3. When some of the Ferric ions in the crystals are substituted by Chromium ions, the green color characteristic of demantoid garnets are produced. However, sometimes the color of Ferric ions manifest itself in the crystal, producing the yellowish-green shades of demantoid and demantoids with a brownish cast.
Finished demantoid garnets are generally under 1 or 2 carats in size. Demantoid garnets over 2 carats are rare, and stones over 3 carats are extremely rare. Stones with intense green coloration are highly valued, but lighter stones of yellowish-green color display more fire, associated with the high dispersion of 0.057.
The main sources of demantoid garnets are Russia and Namibia. Other locations where demantoid garnets are found are Lombardy in Italy, Kerman in Iran, and Afghanistan. The most recently discovered source is Madagascar where significant deposits were discovered in 2009.

Thanks Joan for your critical analysis of the Catseye Alexandrite Necklace highlighted by Maryjewel. Your observations are perfectly in order. The catseye alexandrites in the necklace appear to be genuine alexandrites with their characteristic dark green color in daylight and prominent chatoyancy. However, the uniformity in shape, color, and chatoyancy of all the stones in the necklace, is too good to be genuine, unless it was supported by a lab report from a renowned gem-testing laboratory. Further more the registering of a low ppc-value of US$1,785 only for the alexandrites, seem to consolidate the suspicions that the stones are not genuine natural alexandrites, though the absence of a lab report might have contributed to it.

Thanks AnitaP and rashid for your updates. With regards to the question raised by rashid, if a blue sapphire and diamond of equal volumes are considered, the blue sapphire has a greater weight than the diamond. This is clearly related to the difference in the densities/specific gravities of sapphires (corundum) and diamond. The density of sapphire is greater than the density of diamond. While the density/specific gravity of sapphire (corundum) is 4.0-4.1 gm/cm³, the density of diamond is 3.51 gm/cm.³ In otherwords, while 1.00 cm³ of sapphire weighs 4.0 to 4.1 gm, 1.00 cm³ of diamond weighs only 3.51 gm. Hence, while x cm³ of sapphire weighs 4.0x to 4.1x gm; x cm³ of diamond weighs only 3.51x gm. Thus, equal volumes of sapphire and diamond have slightly different weights, the sapphire weighing more than the diamond.

Conversely, if we take equal weights of sapphire and diamond (M gm), the sapphire will have a slightly lesser volume than the diamond. In other words, the sapphire will be slightly smaller in size than the diamond. Volume= Mass/density. Volume of sapphire = M/4.1; Volume of diamond = M/3.51.

The classification is actually arbitrary based on prices achieved at public auctions. There may be discrepancies in this classification, such as a high-grade blue sapphire falling under medium or low grade, as the price achieved was affected by some factor other than quality-determining factors, such as the smaller size of the gemstone or vice-versa, a medium or low-grade sapphire falling under high-grade, as price was escalated due to historic provenance. Nevertheless, broadly speaking the price-based classification will agree with the quality-based classification, as prices of sapphires are usually determined based on quality factors, such as the hue, tone and saturation of the color and the perfectly symmetrical cut to suit the shape and size of the stone. In the case of Kashmir blue sapphires, the verification of the country-of-origin as Kashmir, itself gives a big boost to its price-per-carat value, but this does not affect the grade classification above, as we are dealing only with Kashmir blue sapphires.