Tanzanite

[varietà gemmifera della ZOISITE]

It was discovered in the sixties in East Africa, among the new gems discovered in that period, it was certainly the most successful.The blue – violet gem of this ZOISITE was discovered in Africa in 1967 and named in honor of the country where it was discovered. discovered by the Tiffany jewelry in New York that put it on the market in ’69.

Its blue or violet color is often comparable with the best Sapphires. Lighter Tanzanites display a delicate periwinkle color, which is extremely rare as they are found in one place in the world in Tanzania’s Merelani Hills. New extraction techniques and the liberalization of the market in Tanzania have made possible a greater availability of gems on the international market. When the stone is found in its matrix the bronze color is dominant. However with modest heating, the cutter can see the blue color bloom and become more intense in the stone.

Legend has it that the effect of heat was discovered in some brown zoisite crystals that were on the ground with other rocks, when they were lapped by a fire lit to clean up herbs in an area of ​​the Merelani Hills, near Arusha in the north of Tanzania. The Masai shepherds who led the herds in that area noticed the blue crystal and picked it up. The color of Tanzanite is more intense in stones weighing more than one carat, the smaller ones are generally more delicate. Gems that show the prevalence of blue instead of violet are usually more expensive, (the cutter had to sacrifice part of the raw material by cutting the gem along the shortest direction to highlight the blue axis color corresponding to the shorter side of the stone raw), so it is inevitable that blue Tanzanites are more expensive, but the color is so beautiful that it is worth the expense.

Tanzanite jewelry is very delicate (gems ​​do not have a great hardness), and you should never clean Tanzanite jewelry with ultrasound. You should never repair a ring with Tanzanite without removing the stone because it could shatter under the heat of a torch. Virtually all blue Tanzanites have been heat treated to improve their color and heating is a commonly accepted practice on the market. Tanzanite has never been synthesized, but there are many materials that imitate it more frequently with blue-violet glass, and it has also been imitated with synthetic Forsterite.

Tourmaline

[Ciclo Silicati – trigonale – AX3Y6(BO3)3Si6O18(O, OH, F)4 A = Ca, Na (K,Cs) ; X = Al,Fe,Li,Mg (Mn) ; Y = Al (Cr,Fe,V) – Hm: 7-7,5 Ps: 2,98-3,25 g/cm3 – Ir: 1,616-1,652]

Tourmalines are a group of complex aluminum borosilicates in which many metals can coexist and replace each other: they are therefore a family of mineralogical terms that crystallize in the same forms and have approximately the same physical constants. Thanks to all these possibilities of chemical substitutions they show virtually any color, and are often found in polychrome crystals.
They have higher dispersion than Topaz and Beryl, but not high enough to compete with the Fire of Diamonds and Zircon. The birefringence and pleochroism are high and are an excellent means of identification of Tourmalines, which also present the phenomena of Piezoelectricity, Pyroelectricity and are also excellent polarizers. If subjected to heating between 450-650 ° C they vary slightly in color, but it is not sure that this treatment will provide improved gems.

Frequent “icy” inclusions frayed with liquid-gaseous fluids that often give a velvety appearance, solid inclusions are generally lepidolite micas, more rarely microcrystals of garnets and zircons. Those inclusions with parallel channels can assume particular importance, which if abundant can give an interesting chalking effect, from which cabochons of CAT EYE TOURMALINE are cut.

The name TORMALINA comes from the Sinhalese “Turmali” which means “mixed”, no other gem can boast the colors that tourmaline can have. Many Russian crown jewel stones that were thought to be rubies have been reclassified as Tourmalines. The last Chinese empress Dowager Tzu Hsi loved pink tourmaline enough to buy at least a ton of it from the new Himalaya Mine in California, which is still in production today. Tourmaline is also of interest to scholars because it changes its electrical charge when heated. It becomes a polarizing crystalline magnet to attract light objects. This property was known long before science was able to explain the phenomenon. Tourmaline can have any color of the iris and combinations of 2 or 3 colors can coexist in polychrome Tourmalines. Sometimes the colors are at the different ends of the crystal. Sometimes one color is in the center of the crystal and the other or others surround it. As in the so-called “Watermelon Tourmalines” WATERMELON TOURMALINE where a central core of pink tourmaline is surrounded by a more or less yellow white band and a green outer ring. Any shade of tourmaline can be found in Brazil, especially in Minas Gerais and Bahia, the most popular are green and pink.

In 1989 tourmalines were discovered like never before. The new type of tourmaline, which soon became known as PARAIBA TOURMALINE, had an incredibly bright blue or green color, the demand and excitement for these new tourmalines quickly caused the cost of the finest stones to rise to over $ 10,000 per kt. Pink and green tourmalines are currently widely available on the market while blue ones are quite rare due to high demand. Tourmalines are often cut in Baguettes that respect their elongated and narrow crystalline habitus, they also show a strong pleochroism: the darkest color is always observed along the axis of the crystal. But for the important gems the classic Cushion cut (or Antique cut) is preferred.

Among the most beautiful tourmalines we must mention a 111 ct pink Manchurian gemstone and two 125 and 173 ct champagne-colored yellow tourmalines, exhibited at the Smithsonian Institution in Washington, as well as various Chinese or Russian sculptures and engravings present in the main collections of the world. In addition to Brazil, tourmalines are found in Tanzania, Kenya, Madagascar, Mozambique, Namibia, Afghanistan, Pakistan, Sri Lanka and in the USA, California and Maine.

A particularly beautiful variety is CHROMOTORMALINE a rare type of tourmaline from Tanzania. Tourmalines are hard and durable gems that are always in fashion but you must be very careful not to clean them with steam or to bring them close to heat sources. In addition, attention must be paid to the edges that can chip. Like the range of colors it presents, the treatment possibilities for tourmaline are many, the resulting stones are stable under normal conditions and totally safe. The most common treatments are coloring, in some cases also irradiation. More rarely, tourmalines are infused with oils to hide fractures and other cracks that reach the surface. Tourmaline has never been synthesized but is imitated in many ways from similar natural stones to artificial glass pastes.

Mineralogists distinguish various members of the mineralogical family of tourmalines:
– SCIORLO or also SCIORLITE (Borosilicate Sodium and Iron hydroxide) or Black Tourmaline
– ELBAITE (Sodium and Lithium Hydroxide Borosilicate) generally dark green almost black, but it is the gemmiferous member of tourmalines;
– DRAVITE (Borosilicate sodium, magnesium and aluminum hydroxide)
– UVITE (Borosilicate hydroxy-fluoride of Calcium Sodium Magnesium and Iron)
– BUERGUERITE (Sodium Iron and Aluminum Hydroxy-fluoride Borosilicate),
– FOITITE (Borosilicate iron and aluminum hydroxide),
– CROMODRAVITE (Borosilicate hydroxy-fluoride of Sodium Magnesium Chromium Iron and Aluminum),
– FERUVITE (Borosilicate Hydroxide of Calcium Iron Magnesium Aluminum),
– LIDDICOATITE (Sodium Lithium and Aluminum oxy-hydroxy-fluoride borosilicate),
– OLENITE (Sodium and Aluminum oxyhydroxide borosilicate),
– POVONDRAVITE (Sodium and Iron oxyhydroxide borosilicate).

From a gemological point of view, the following varieties are of some interest. All the precious gem-bearing varieties are generally referable to ELBAITE, the traditional green or polychrome tourmaline, apart from the relatively rare case of green gems cut from UVITE crystals, and to DRAVITE which provides yellow-brown gems.

– colorless variety: ACROITE of pure collector’s interest.
– red variety: RUBELLITE
– pink / purple variety: SIBELLITE
– green variety: VERDELITE
– CHROME-TOURMALINE sub-variety of Verdelite with the typical bright coloring of chrome.
– Blue variety: INDICOLITE.
– yellow variety: DRAVITE
– Polychrome variety: TWO-COLOR, TRICOLOR
– WATERMELON TOURMALINE: polychrome variety in which between the central pink part and the green border there is a thin white band
– PARAIBA TOURMALINE: Very rare tourmaline which is one of the Must of international jewelry.

PARAIBA TOURMALINE (en: Paraiba Tourmaline)

Talking about the Paraiba Tourmaline in gemology is like talking about the Phoenix. Copper and manganese (and a recent study would indicate a high concentration of traces of Gold) seem to be responsible for the colors of Paraiba.The combination of these two elements causes a wide variety of beautiful and fascinating colors in Paraiba tourmalines: emerald green, turquoise. – sky blue, sapphire blue, indigo blue, purple blue, purple red known among traders as Paraiba blue and Paraiba green and neon blue or neon green or even electric blue and electric green. In mineralogy we can define it as an ELBAITE CUPRIFERA.

These small, rare and precious tourmalines were mined in Sao José da Bathalha in the Brazilian state of Paraiba. The “Paraiba” was discovered in 1987: its discovery is due to a man and his unshakable faith, Heitor Dimas Barbosa who for years had dug with his helpers a small hill where a pegmatite emerged near the town of Sao José da Bathalha. Heitor Dimas Barbosa was not only a gem hunter he was deeply convinced that under the famous hill there was something “completely different” and his vision turned out to be correct. Since 1981 he had begun excavating in the old abandoned mines, suddenly, five and a half years after the first excavation, the first deposits of tourmaline appeared and in the fall of 1989 a handful of the finest tourmaline crystals were unearthed by one of the many dark passages. These crystals displayed colors never dreamed of before.

A high concentration of copper is responsible for the highly sought-after bright blue, turquoise and green, while red and green are caused by manganese. By heating the stones, expert cutters are able to eliminate traces of red, so that only the brilliant copper color appears.

The exceptionally vivid color of Paraiba tourmalines can only be appreciated after the gem has been cut. When it has been faceted, it exhibits a unique luster and brilliance, which makes the gem shine and shine even when the light is poor. Therefore, the color is often referred to as “Electric” “Fluorescent” or “Neon”.

The history of Paraiba should end here, but nature always has some surprises in store in fact at the beginning of 2001, suddenly, stones from Nigeria, tourmalines of a brilliant bluish-green, similar to those of Paraiba, appeared on the market. These stones, like Paraiba tourmalines, showed their true beauty after being carefully heated. Generally, their colors seem slightly more muted, but the difference is hardly discernible by anyone who is not an expert and even scientists find it difficult to define the existence of different characteristics between the Nigerian and Brazilian Paraibas. Copper-containing mines explain the similarity in chemical composition. Both types owe their color to copper and manganese. But this example of a valuable gem clearly illustrates the phenomenon of continental drift. Present-day Nigeria was originally directly connected with the north east of Brazil. So it is easy to assume that the tourmalines of Paraiba and Nigeria formed under the same geotectonic conditions, before the two continents separated.

Aquamarine

[Berillo blu > Ciclo silicato]

Color: Blue, greenish blue, green

  • Mohs hardness: 7.5
  • Refractive index: 1.57 – 1.59
  • Density: 2.67 – 2.75
  • Chemical Formula: Be3Al2(SiO3)6
  • Crystal: hexagonal
  • Luster: vitreous
  • Origin: Brazil, Madagascar, Mozambique, Russia, India, Sri Lanka, China

Blue variety of Beryl, known in all shades of blue, with more or less green shades, up to almost colorless shades, it can take on all shades of the sea. As the name implies, it is the gem of the sea. The blue color is attributed to traces of iron in the crystal lattice. AQUAMARINA always has a light blue color, but the darker the color, the more the gem is worth. Connoisseurs prefer pure blue stones, without green hues. Since the color is generally clear to have a beautiful stone we must find them very pure.

The main cuts are oval and emerald.
ACQUAMARINA is found almost everywhere in the world but the most beautiful samples come from Brazil, Zambia, Mozambique, Angola, Nigeria, Russia.

Mineral of good hardness and which does not require special care for conservation and cleaning. The most frequent treatment to which the gem is subjected, which is normally accepted, is heating to make the blue color more intense and homogeneous, however only extremely pure stones can be treated, in fact the presence of inclusions and other defects is easily detected. because of the transparency of the gem.

Being one of the classic gems it has always been at the center of attempts at imitation or falsification. The stone with which it is most often imitated is blue topaz, especially since it is possible to produce large quantities of topaz thanks to the heating technique, such falsifications are easily revealed with the various filters: Chelsea, etc. It is more difficult to try to replace it with other stones for various reasons: the Tourmaline always has greenish shades and perhaps an aquamarine-colored tourmaline would be even more rare and precious, spinels, sapphires and zircons are either much darker or much brighter, but because they are produced large quantities of synthetics deception is always possible. Speaking of synthetics: some imperfections in the stone and often a guarantee of naturalness. (generally the defect of synthetics is the perfection of the product).

The minerals and various materials with which the aquamarine is imitated are:

  • Blue Topaz – easily distinguishable with “Chelsea” filters, etc.
  • Blue Quartz – stands out with filters
  • Spinel
  • Blue apatite, hardness and appearance
  • Natural or synthetic sapphire
  • Tourmaline
  • Tanzanite
  • Blue zircon: appearance and weight
  • Blue glass (Cobalt): filters
  • Clear glass pastes: filters
  • Dark glass pastes: filters
  • synthetic spinels (cobalt)
  • Doubles of Garnet

A bad quality of bluish quartz was marketed in Central Europe under the name of Aquamarine of Saxony.