Chemical Formula: Al2Si03; Aluminum silicate
Crystal Structure: Orthorhombic; thick-columnar
Color: Yellow-green, brownish-red, green
Color of Streak: White
Hardness: 7.5 on the Mohs scale
Refractive Index: 1.627 – 1.649
Density: 3.05 – 3.20
Cleavage: Good; uneven fracture
Transparency: Transparent to translucent, opaque
Absorption Spectrum: 553, 550, 547, 525, 518, 495, 455, 447, 436
Double Refraction / Birefringence: -0.007 to -0.013
Luster: Vitreous to matte
Fluorescence: Weak: green, yellow-green
Andalusite is a lesser-known gemstone named after a Spanish autonomous community where it was first discovered, Andalusia. By composition, andalusite is an aluminum silicate closely related to both sillimanite and kyanite. In fact, all three minerals are polymorphs, which means they share the same chemical composition, but possess different crystal structures. Andalusite is a strikingly beautiful gem, but it is largely unknown to the general public and considered to be one of the lesser-known gem types in the trade.
Andalusite gemstones are found in very distinct combinations of colors, and a very pronounced level of pleochroism, which results in the exhibition of different colors when viewed from different angles. The attraction and new-found appreciation for andalusite is greatly owed to its unmistakable and unique twist on play of color. For many years, andalusite has primarily been a collector’s stone, but it has recently gained a lot of attention from many jewelry designers.
There are only a few gem types that could be mistaken for andalusite, including tourmaline, chrysoberyl, sphene, smoky quartz and idocrase. Pleochroism in gems occurs in varying strengths; weak, distinct or strong. Pleochroic effects are the result of differing absorption of light rays, and the phenomenon can only occur with doubly refractive crystals. Andalusite is considered to be strongly pleochroic, along with iolite, kyanite, kunzite, sphene and tanzanite. Andalusite has trichroic pleochroism; when light enters the stone, it is parted into three sections, each containing a portion of the visible spectrum. Some pleochroic gems, such as kunzite, possess dichroic pleochroism, which means that they display only two different colors. Andalusite has a Mohs hardness rating of 7.5; slightly higher than that of quartz.
Andalusite Origin and Gemstone Sources
Andalusite typically occurs in placers, gneisses, and schists as a result of argillaceous sediment that has been metamorphosed. Andalusite rarely occurs in granite or pegmatites, but when it does, it tends to yield the largest crystals. Andalusite deposits can be found in many locations, including Australia, Brazil, Canada, Russia, Spain (Andalusia), Sri Lanka, Burma, Madagascar and the USA (California and Colorado).
Andalusite colors depend on the orientation of the crystal, but it typically occurs in yellow, yellow-green, green, brownish-red, olive and reddish-brown. Most stones exhibit two colors that differ in intensity, and often times, colors blend together, which is especially seen in square and round-cut gemstones. Shapes with a long axis, including ovals, pears, marquise and emerald-cuts, tend to show one color near the center and a darker second color toward the ends of the crystal. Typically, when cutting pleochroic gems, cutters attempt to minimize pleochroism and maximize one desirable color. However, with andalusite, cutters do the exact opposite and try to orient the gem to result in a pleasing mix of colors, such as orangey-brown and yellowish-green or gold.
Andalusite Clarity and Luster
Andalusite typically occurs translucent to opaque, with transparent gemstone-quality specimens being very rare. Opaque specimens are known as chiastolite. Dark inclusions in chiastolite produces cruciform-like shapes within the stones and these are often referred to as ‘Cross Stones’. Chiastolite usually occurs white, gray or yellowish and is rather soft (5 – 5.5 on the Mohs scale) compared to transparent andalusite. Transparent andalusite makes up only a small percentage of gemstone-quality yield. Almost all andalusite gemstones will contain visible inclusions, often rutile needles. When polished, andalusite has a vitreous to matte luster.
Andalusite Cut and Shape
Andalusite is almost always faceted, often with brilliant cuts and very rarely cut en cabochon, with exception to opaque material. Andalusite color can be greatly enhanced through proper orientation and quality cutting. Without proper cutting, andalusite would not display its desirable pleochroic shades of brown, green and reddish-brown. Oval, marquise and emerald cuts are very popular, due to their long axes. Square and round cuts are also popular because they will have an attractive mosaic-like blend of colors. Since andalusite is one of the lesser-known gemstones, trillions, hearts and other fancy shapes are not very common because there is little demand for them.
Andalusite is typically untreated. Some Brazilian material is known to change from olive-green to pinkish when heated, while some brown specimens can fade to colorless when heated above 800Â°C. Any treatments or enhancements should be openly disclosed by gemstone suppliers.
Only a few gem types could be mistaken for andalusite, including tourmaline, chrysoberyl, sphene, smoky quartz, idocrase or sinhalite. Due to distinct markings, it is very difficult to imitate because of its pronounced pleochroic properties. Tanzanite, iolite and kunzite also have similar pleochroic properties. Chiastolite, an opaque variety of andulusite, is not nearly as desirable or popular as transparent, gem-quality andalusite. Kyanite and sillimanite are popular gemstones that share the same chemical composition, albeit differing crystal structures.
Most Popular Related Gemstones
Lesser Known Related Gemstones
Chiastolite (Cross Stone) is an opaque variety of andalusite. Sillimanite cat’s eye is related to both kyanite and andalusite. Sphene, idocrase and sinhalite are also lesser-known, but unrelated; these gemstones can resemble andalusite due to their pleochroic qualities.
Andalusite Gemstone Mythology
As a lesser-known gemstone, andalusite produces mostly blank pages in the books of myth, history, wisdom, astrology (zodiac) and the relationship between the planets and mankind. Although there are only a few myths specific to andalusite, it has been worn as amulets for quite some time, which suggests that many older cultures believed in its crystal powers. Andalusite was likely used for ceremonial purposes and alternative healing practices.
Andalusite is sometimes referred to as the “Seeing Stone”. It earned this name due to its metaphysical ability to calmly see, without bias, various aspects of character. Andalusite is sometimes used to encourage its wearer to appraise issues rationally and to see problems from all perspectives, without fear or judgment. Andalusite helps its wearer to realize that self-sacrifices are never required, but are acceptable when needed. Andalusite is believed by some to help with HIV (AIDS), eye disorders and is said boost calcium, oxygen and iodine levels. Andalusite is also thought to relieve water retention, enhance memory, encourage chivalry, balance and moderation in its wearer. Andalusite is used as a meditation and centering stone. Additionally, it is a stone of Virgo and it is primarily associated with the 3rd and 4th chakras (the solar plexus and heart chakras).
Andalusite Gemstone and Jewelry Design Ideas
As of recently, andalusite has become increasingly more popular when it comes to gemstone jewelry designs. Andalusite possesses a good level of durability and hardness, making it suitable for any type of jewelry application. Andalusite possesses a good level of durability and hardness, making it suitable for any type of jewelry application. It has a hardness rating of 7.5 on the Mohs scale of hardness, making it harder than quartz. Andalusite crystals are not commonly found in large sizes, so they are most commonly used as accent stones or in cluster designs for colored stone jewelry. It is also ideal as the center stone for rings, bracelets, necklaces, brooches, cuff-links, tie-tacks and pendants. Due to its pleochroism, it is best suited for jewelry designs that allow light to strike the stone at many angles. Closed settings will not allow andalusite to display this desirable quality.
Andalusite Gemstone and Jewelry Care and Cleaning
Andalusite is quite durable and can be wiped down using any soft cloth or soft-bristled brush. A mild soap or detergent can be used, but should be rinsed well to remove soapy residue. Andalusite has an uneven fracture and good cleavage, so it is not as sensitive to blows as some other stones, such as tanzanite, topaz and diamond; however, andalusite should be protected from any hard blows to prevent fracturing. As with almost all colored stones, avoid the use of harsh household chemicals. When storing andalusite, it is best to store the jewelry or gemstone wrapped in a soft cloth or inside a fabric-lined box. To preserve andalusite polish and to prevent surface scratches, always store andalusite separately from other gems.
Original article: Andalusite
I’ve always loved andalusite.