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The “Deceptive” Gemstone—Apatite

Apatite, whose name is derived from the Greek word meaning “deception,” is so named because its color and luster often resemble other gemstones. Apatite is a group of calcium phosphate minerals that contain chlorine or fluorine, with the main types being fluorapatite and chlorapatite. It comes in a variety of colors, including colorless, yellow, blue, purple, green, brown, and white, and may exhibit phosphorescence and strong pleochroism. Apatite is found in igneous, metamorphic, and sedimentary rocks, with gem-quality apatite mainly coming from pegmatites and alluvial deposits. Despite its relatively low hardness, making it less favored by jewelers, apatite is an important industrial mineral for extracting phosphorus, which is widely used in the medical, chemical, and other industries. When selecting apatite gemstones, flawless and brightly colored stones are the most desirable, especially those with a cat’s eye effect. While apatite is resistant to impact, it is susceptible to damage from acids, so proper care must be taken to avoid exposure to acidic substances.

Rare gemstone variety – Danburite

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Danburite is a kind of rare gem, the English scientific name comes from its discover location—Danbury, Connecticut, USA, the Chinese name is derived from its appearance, which is similar to topaz. It’s primarily found in pegmatite and metamorphosed carbonate rocks that are rich in cryogenic hydrothermal fluids, coexist with plagioclase and orthoclase in dolostone. Danburite can be found in colors ranging from colorless, light yellow, brown, to the rarer pink and purple. Commercially, the appearance and index of refractive of danburite are both similar to those of topaz, but danburite can be identified by its low specific gravity, fluorescence and low birefringence index. Most danburite appear gray and opaque, with gem-quality transparency being extremely rare, but even so most enthusiasts still value its natural appearance and regard it as collection. Danburite has high hardness and toughness, doesn’t require special maintenance in both collection and wear, makes it relatively easy to care.

The Art of Nature——Aragonite

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Aragonite, named after Aragon, Spain, is composed mainly of calcium carbonate with manganese and iron. Despite its similarity to calcite, it is rarer in nature and less chemically stable, often converting into calcite. Both onyx and ammolite are aragonite-based gemstones, with onyx being used for decorative purposes, and ammolite admired for its vibrant colors and pattern distribution.

Advanced Refractory Materials — Kyanite

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The English name “Kyanite” for blue kyanite comes from the Greek word meaning “blue.” Kyanite is a regional metamorphic mineral belonging to the triclinic crystal system, and its colors are often vibrant blue but can also include light blue, dark blue, and other shades. Due to its varying hardness along different axes, it is known as the “two-hardness stone.” Although kyanite is not highly valued commercially, its color rivals that of premium sapphires. Ideal selections have vivid colors and appear flawless to the naked eye. In industrial applications, kyanite is highly refractory and used to produce advanced refractory materials and ceramics, widely utilized in industries such as automotive and aerospace.

Advanced Refractory Materials — Andalusite

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Andalusite is a metamorphic mineral with the chemical composition of aluminum silicate (Al₂SiO₅) [Al2SiO5] .Under varying temperature and pressure conditions, it can transform into kyanite or sillimanite, making these minerals polymorphs. Andalusite becomes mullite, a high-alumina material, at 1380°C and can withstand temperatures as high as 1800°C. It exhibits strong pleochroism, showing red, yellow, and green when viewed from different angles. When selecting andalusite, those with bright colors and pronounced pleochroism are preferred. Large stones over 2 carats are rare and considered collectible. Its Mohs hardness is 7.5, and it is typically reddish-brown and highly transparent. Andalusite crystals showing a “black cross” pattern on the surface are known as chiastolite.

Metamorphic Rock Companion – Tanzanite

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Tanzanite was discovered in 1967 in northern Tanzania and was initially mistaken for sapphire before being recognized as a new gem. Gem-quality blue tanzanite was promoted by Tiffany & Co., with deep blue and indigo hues being the most prized. Tanzanite exhibits strong pleochroism, meaning its color can vary depending on the cutting direction. In Taiwan, tanzanite entered the market around 1995, initially as a substitute for sapphire due to its similar color. Thanks to Tiffany’s efforts, tanzanite has since gained recognition as a unique and rare blue gemstone, with prices around NT$10,000 to NT$15,000 per carat.

Octahedral Crystal – Spinel

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The English name for spinel comes from the Latin word “Spina,” meaning “little thorn,” due to the eight-pointed structure of its octahedral crystal. The blue and red varieties of spinel resemble sapphire and ruby, respectively. In the past, red spinel was often mistaken for ruby, such as the British Royal Family’s Timur Ruby and the Black Prince’s Ruby, both later identified as red spinel. The commercial value of spinel depends on its color and clarity, with the most valuable being those closest to pure red or blue. Chromium-rich red spinels and cobalt-rich blue spinels are highly priced and usually require no enhancement. Spinel has high hardness, good toughness, and excellent chemical stability, making it a popular choice in the market.

Blue-Green Jade – Tourmaline

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Tourmaline is renowned for its wide range of colors, with its name derived from the Sinhalese word “TURMALI.” Tourmaline crystals possess both piezoelectric and pyroelectric properties, generating electrical charges when subjected to pressure or heat. Among the various colors, blue or blue-green tourmalines are the most valuable, followed by red, while chrome tourmaline with a bright green color also holds high value. The rarest and most valuable is Paraiba tourmaline. When selecting tourmaline, the 4C principles (color, clarity, cut, and carat) play a key role in determining its price. Cat’s eye tourmaline is a rare phenomenon. High clarity and well-cut stones are more valuable.

Australia’s National Gemstone – Opal

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Opal is the birthstone for October and the national gemstone of Australia, renowned for its vibrant play of colors, referred to as opalescence or play of color. Opals are categorized based on their base color into white opal, black opal, fire opal, and crystal opal, with black opal being the most valuable. Boulder opal, which is opal cut with its host rock, is less expensive but can still exhibit a strong play of color. The play of color in opals comes in three patterns: pinpoint (small dots), broad flash (large patches), and harlequin (angular shapes), with red flashes being the rarest and most valuable. The quality of the play of color is the primary factor determining the value of an opal.

Organic Gemstone——Pearl

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Introduction Pearl is an organic gemstone, meaning it is entirely formed from biological processes. Unlike inorganic gemstones that are mined from the earth, organic gemstones like pearls are created as a protective response by living organisms. Pearls are formed by the calcium secretions of mollusks, which coat foreign particles entering their shells. Pearls can be …

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