Mohs scale hardness: 8.5
Chrysoberyl is composed of beryllium aluminium oxide. The name chrysoberyl comes from the Greek which means "gold-colored beryl" but in fact chrysoberyl and beryl are two completely different gemstones. In terms of hardness, chrysoberyl is much more harder than beryl. Although both minerals contain element glucinum (berllium) but chrysoberyl has no silica in its composition, as has beryl. Chrysoberyl composed of glucina and alumina, the perentages being alumina 80.2, glucina 19.8. however, some other oxides might be present as impurities or replacing the alumina (iron and chromium oxides for example).
Chrysoberyl has a prismatic cleavage and conchoidal fracture. The mineral is infusible and is not attacked by acids. Its luster is vitreous, tending to oily, and is brilliant. Chrysoberyl is usually yellow-green, brownish or yellow with its color being caused by the presence of iron. The strong band will usually be revealed by spectroscopic analysis, where the violet takes over from the blue. When the color darkens from bright yelowish-green to golden-yelow to brown, this band increases in strength. Two additional bands can be seen in the green-blue if the stone has a strong color. Liquid-filled cavities containing three-phase inclusions are the most common inclusions. Stepped twin planes may be apparent in some cases.
An interesting feature of its crystals are the cyclic twins called trilling. Thise twinned crystals have a hexagonal apearance, but are the resullt of a triplet of twins witth each "twin" taking up 120 degrees of the cyclic trilling. Chrysoberyl is the third hardest natural gemstone and lies between corundum and topaz on Mohs hardness scale. Chrysoberyl was first described and named by Abraham Gottlob Werner (a famous German geologist) in 1790, a year after it was discovered.
There are three main gem varieties of chrysoberyl and they each offer a different type of beauty:
The first one is the ordinary yellow chrysoberyl. During the Victorian and Edwardian eras this yellow chrysoberyl was referred to as chrysolite, that name is no longer used in the gemological nomenclature. Ordinary chrysoberyl is greenish-yellow and transparent to translucent. It is used as a gemstone when the mineral exhibits nice pale green to yellow color and is transparent.
The second variety is "cat's eye" also known as cymophane. Cymophane comes from the Greek words cyma and phanes, which mean “wave” and “appearance”. This variety exhibits beautiful opalescence or chatoyant that reminds one of an eye of a cat. When cut into cabochon, this mineral forms a light-green specimen with a silky bband of light extending across the surface of the stone.
The third and perhaps most interesting is alexandrite. A strongly pleochroic (trichroic) gem, will exhibit red, orange-yellow and emerald green colors and tend to change color in artifical light compared to daylight. A strong absorption of light in the blue and yellow portions of the spectrum results in color changing from red to green. Typically, alexandrite has a color of an emerald-green in daylight but exhibit a color of raspberry-red in incandescent light.
Of the three chrysoberyl, alexandrite is the most expensive, followed by cat's eye and lastly, yellow chrysoberyl.
How Chrysoberyl is Formed
Chrysoberyl was formed as a result of pegmatitic processes. The processes occured at least 250 million years ago. The molten magma was forced by the high pressures and temperatures from the outer layers of the earth's mantle towards the surface. As the main magma body cooled, water originaly present in low concentrations became more concentrated in the moltenn rock because it could not be incorporated into the crystalization of the localized minerals. Consequently, the remaining portion of these molten magma was water rich. It was also rich in silica and rare elements that still had not solidified. During the final stages of the crystallization, this water-rich magma was expelled. It was then solidified in cracks and crevasses to form a pegmatite.
Iff the pegmatite magma was rich in beryllium, crystals of chrysoberyl and beryl could form, but some chromium would also have had to be present in order for alexandrite to form. Since chromium and beryllium are extremely rare elements in rocks, this is only proces which could have concentrated these unusual elements in environment where crystallization could occur.
The possibility for the crystals to grow quickly was contributed by the high water content of the magma, therefore pegmatite crystals are often quite large and of course for gem specimens this factor is important. Chrysoberyl is always accompanied by quartz. It occurs in mica schists and granite pegmatites and in contact with metamorphic deposits of dolomitic marble. Itt is also recovered from river sands, gravels in alluvial deposits with spinel, corundum, garnet and tourmaline.
It is believed chrysoberyl have special properties:
- To protect its wearer from dangers.
- Be able to transform negative energy into positive one.
- To promote tolerance, peace and harmony.
- Used as good luck charm in numerous cultures.
Chrysoberyl cat's eye perfectly mimics the ghostly appearance of the eye of a cat caught in a pair of headlights at night. The stone comes in two colors: translucent honey brown and apple green, and is cut into high-domed cabochons. A silken-sheened slit of silvery white glides across the face of the dome whenever the gem is tilted slightly, widening and narrowing like the iris of a cat's eye.
This eerie effect is caused by tiny, hair-like inclusions reflecting in the light and is known as chatoyancy (chatoyancy comes from the French words: chat for cat, oeil for eye). The inclusions of the stone are aligned parallel to the crystallographic axis and are always cut as cabochons with the fibrous needle-like inclusions running across the narrow part of the stone, this is the only way to display the effect properly. While this characteristic appears in other gems, none has the clarity and impact of cat's eyes in chrysoberyl. Milk and honey is a term commonly used by gemologists to describe the color of the best cat's eyes. Chrysoberyl lacking the silky inclusions required to display the cat´s eye effect is usually faceted.
Chrysoberyl cat’s eye is not the only stone which display this chatoyancy, other minerals such as corundum, tourmaline, scapolite, quartz, spinel etc also have this feature. The industry designates these gemstones as ruby cat's eyes, or quartz cat's eyes, sapphire cat’s eye etc and only the chrysoberyl gemstone can be refered to as cat's eye with no other designation. Chrysoberyl that does not show a cat´s eye or a color change is known simply as chrysoberyl.
The value of a chrysoberyl cat's eye is determined by the sharpness of the eye and the richness and luster of the stone's color. Some chrysoberyl cat's eye exhibit what is known as a milk-and-honey effect. When a pen light is aimed at the side of the stone, one half will appear milky white, while the other half remains gold. Chrysoberyl cat's eye is a favorite stone for men's rings and cuff links. Cat´s eye material is found as a small percenttage of the overall chrysoberyl production wherever chrysoberyl is found. Cat's eyes are sometimes irradiated in order to improve color and chatoyancy. One of the best way to clean the gemstone is by using warm soapy water and a soft brush.
The gemstone alexandrite is a chrysoberyl containing iron, chromium and titanium as impurities. It is the color-changing variety of the mineral chrysoberyl and is one of the rarest gemstone in the world as unique geological conditions were needed for its formation. Alexandrite has the unique property of exhibiting different colors depending on the time of the day. It looks green in daylight and reddish purple in artificial light. The changing color properties is attributed to the presence of chromium.
Stones with a weak change or better are considered as alexandrite, while stones with a faint change are considered as chrysoberyl. The color change is caused by alumunium impurities in the gemstone being displaced by chromium oxide. Alexandrite is scarce because of its requirements for two kinds of minerals (one providing beryllium and aluminium and the other providing chromium oxide) that gives the stone the ability to change colors in different light. At the same time, silica is not present where alexendrite is found. This is critical since silica is the 2nd most common element in the earth’s crust. The color of the gemstone can also shift depending on your viewing angle, this phenomenon is known as pleochroism.
This rare gemstone was discovered on the Czar Alexander's 16th birthday and named in honor of the future Russian Tsar Alexander II. Alexandrite was the national stone of tsarist Russia as the dual colors of the stone red and green were important colors of imperial Russia. Alexandrite is the birthstone for the month of June. Beside Alexandrite, the other birthstones for June include pearls and moonstone. Alexandrite was considered widely as a symbol of good luck, it is believed to strengthen the intuition of those who wear it. It is also the anniversary gemstone for the 45th and 55th years of marriage.
The beautiful changing color qualities, the rarity of the stone plus a good hardness (8.5 in Mohs scale) make alexandrites one of the most expensive gemstones in the world.
Astrologically, alexandrite is associated with the zodiac signs of Gemini
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