Chrysoberyl Vartries

Gemstone Types and Characteristics

• Alexandrite: rare, faceted mixed cut, exhibits color change, also known as "emerald by day, ruby by night"
• Cat's Eye: cabochon with inclusions, fine quality has girdle-to-girdle inclusions, typically 0.50 to 2.00 cts.
• Andalusite: faceted, sizes range from 1 to 10 cts., also known as Chiastolite
• Tanzanite: variety of zoisite, typically faceted, fine quality is pure blue or intense violet-blue
• Iolite: also known as Cordierite, transparent, violetish blue through violet hue, pleochroic colors range from light/dark violet to yellow/yellow-brown and blue gray

Origins and Sources

• Tanzanite: Merelani in northern Africa, near Tanzania
• Iolite: Sri Lanka, several areas of Africa, Kenya, central Tanzania, and the island of Madagascar, India, Brazil, Norway, and Finland
• Alexandrite: Ural Mountains of Russia, Sir Lanka, Brazil, India, Myanmar's Mogok Stone Tract, East Africa, and Madagascar
• Cat's Eye: Sir Lanka, Brazil, Myanmar's Mogok Stone Tract, Zimbabwe, Madagascar, and Tanzania
• Andalusite: Brazil, Sri Lanka, and Spain

Synthetic Processes

• Tanzanite: synthetic forsterite is used as synthetic tanzanite due to its pleochroic qualities
• Alexandrite: produced using "Czochralski", floating zone, and flux methods
• Green Chrysoberyl: vanadium is used to produce bluish green, nonphenomenal, pulled synthetic chrysoberyl

Physical Properties

• Tanzanite: Mohs scale 6 to 7
• Iolite: Mohs scale 7 to 7.5
• Alexandrite: Mohs scale 8.5
• Andalusite: Mohs scale 7 to 7.5

Phenomena and Characteristics

• Tanzanite: exhibits pleochroism
• Iolite: exhibits pleochroism
• Alexandrite: exhibits color change or "the alexandrite effect" and cat's eye
• Cat's Eye: exhibits chatoyancy and pleochroism
• Andalusite: exhibits pleochroic colors, also hues of olive or brownish green, yellowish green, and brownish red

Tanzanite

• Named and promoted by Tiffany's in 1968
• Found in Merelani, northern Africa, near Tanzania
• Variety of zoisite
• Fine quality is pure blue, intense violet-blue, or violet body color
• Has a Mohs scale hardness of 6 to 7
• Often heat-treated to enhance color

Iolite

• Also known as cordierite
• Found in Sri Lanka, Africa, India, Brazil, Norway, and Finland
• Transparent, violetish blue to violet hue
• Has a Mohs scale hardness of 7 to 7.5
• Often found in alluvial deposits

Alexandrite

• Variety of chrysoberyl
• Found in Ural Mountains of Russia, Sri Lanka, Brazil, India, Myanmar, and East Africa
• Has a strong color change effect, appearing bluish green in daylight and orangy red in incandescent light
• Has a Mohs scale hardness of 8.5
• Often found in alluvial deposits

Cat's Eye Chrysoberyl

• Type of chrysoberyl with a distinct, straight, silver-white chatoyant band
• Found in Sri Lanka, Brazil, Myanmar, and Zimbabwe
• Fine quality is semitransparent with a golden yellow to slightly greenish yellow or brownish yellow color
• Often cut into a cabochon shape

Andalusite

• Found in Brazil, Sri Lanka, and Spain
• Has a Mohs scale hardness of 7 to 7.5
• Can appear in various colors, including brownish or yellowish green, orange, pink, or violet
• Often found in alluvial deposits

General Information

• Pleochroism is a phenomenon where a gemstone appears to change color when viewed from different angles
• The "Alexandrite Effect" is a specific type of color change phenomenon
• Chatoyancy is a phenomenon where a gemstone appears to have a moving band of light
• Many gemstones are treated or synthetic to enhance their appearance or color

Tanzanite

• Named and promoted by Tiffany's in 1968
• Government control of the mine affects prices
• TV promoted it to US consumers
• Variety of zoisite
• Mohs scale: 6 to 7
• Fine quality is pure blue, intense violet-blue, or strong purplish pleochroic
• Can be heat-treated to turn brown stone to blue and violet

Iolite

• Also known as "Cordierite"
• Transparent, violetish blue to violet hue
• Pleochroic colors range from light to dark violet and yellow to yellow-brown
• Mohs scale: 7 to 7.5
• Found in alluvial deposits
• Cleavage in one direction makes it vulnerable when mounted

Alexandrite

• Variety of chrysoberyl
• Mohs scale: 8.5
• Very strongly bluish green to yellowish green in daylight, and orangy red to purplish red in incandescent light
• Exhibits the "Alexandrite Effect"
• Found in alluvial deposits
• Mainly faceted, always cut to show best color change

Cat's Eye Chrysoberyl

• Chrysoberyl with a distinct, straight, silver-white chatoyant band
• Fine quality is semitransparent, golden yellow to slightly greenish yellow, or brownish yellow
• Can be pleochroic
• Typically 0.50 to 2.00 cts.

Andalusite

• Aluminum silicate
• Mohs scale: 7 to 7.5
• Can be brownish or yellowish green to orangy brown, pure green, brown, pink, or violet
• Finest quality is yellowish green and orange
• Can be pleochroic, with colors tending towards reds, greens, and oranges
• Found in Spain, Brazil, and Sri Lanka

General Information

• Largest consumers of these gemstones are not specified
• Chemical composition: Tanzanite (silica, calcium, aluminum), Iolite (silicate of aluminum, iron, and magnesium), Alexandrite (beryllium aluminum oxide), Andalusite (aluminum silicate)
• Forming sources: Iolite (alluvial deposits), Alexandrite (alluvial deposits), Andalusite (trace elements of iron and titanium)
• Possible phenomena: Tanzanite (pleochroism), Iolite (pleochroism), Alexandrite (color change), Cat's Eye (chatoyancy), Andalusite (pleochroism)