Gemstones Fact Sheet
Amethyst is the birthstone for February
Quartz, found in rocks of all ages and many ore deposits, is the most common of all minerals. Amethyst is the most highly valued stone in the quartz group. It was believed to bring its wearer luck and protect against magic.
It is said to symbolize sincerity. It was used as a charm by the Greeks to prevent drunkenness!
Quartz is a very important rock-forming mineral, being an essential component of many igneous,
metamorphic, and sedimentary rocks. Amethyst crystals always grow from a base.
The most important amethyst deposits are in Brazil, Uruguay, and Madagascar.
Although it is considered a semi-precious stone, amethyst is consistently among the best sellers,
alongside precious stones such as sapphire, ruby, and emerald. No doubt, this is due to its very appealing purple color.
Other stones in the quartz group include:
Citrine - yellow to orange and brown
Smoky Quartz - often erroneously called "smoky topaz", gray-brown
Rock Crystal – colorless
Rose Quartz – pink
Crystalline varieties with inclusions:
Rutilated Quartz- contains rutile crystals
Tiger-eye - usually striped, brown and gold
Aventurine – spangled with mica or hematite, green or gold brown
Chalcedony - cloudy blue, white, gray
Carnelian - reddish brown
Agate - various colors, banded or layered
Onyx - agate, most commonly dyed black
Jasper - various colors, usually striped or spotted
Chrysoprase - pastel green to apple green
Bloodstone - (Heliotrope) very dark green with spots of red
Agatized wood - also known as petrified wood
Opal – although unlike any other -see entry under opal
Mohs’ Hardness: 7
Specific Gravity: 2.63-2.65
Chemical composition: SiO2 silicon dioxide
Refractive Index: 1.544-1.553
Crystal System: Hexagonal (trigonal); hexagonal prisms
Emerald is the birthstone for May.
Emerald is the most precious of the beryl group (aquamarine is also beryl).
The name "emerald" seems to have come from the Persian word for "green stone".
Emeralds are usually considered to be more precious than diamonds. This is due to a large part to their scarcity. Beryllium, an element necessary to form emeralds, is very rare.
Because of the way they grow, emeralds often contain inclusions; bubbles, healing cracks, "carbon" flecks, and foreign crystals. These are not necessarily faults, and they can indicate the genuineness of the stone. A perfectly clean emerald is almost unheard of!
The most desired color is deep green. A stone of this color is more valuable even with inclusions than a clean stone that is pale in color. It’s color is very stable, not changed by light or heat (unless it exceeds 1200F). The pigment that gives an emerald its fantastic green color is chrome or vanadium.
Large deposits are found in Brazil, Columbia and South Africa. Sometimes the particular shade of green can indicate where it is from. Other sources include: Australia, India, Pakistan, Tanzania, the U.S. and Zambia.
For thousands of years, almost all of emeralds came from Egypt. "Cleopatra’s Mines" worked first by the Egyptians, then by the Romans and the Turks, were in nearly continuous operation from about 330 B.C. to 1237 A.D. "This monopoly lasted until the Spanish conquistadores arrived in South America in the early part of the 16th century. Shortly afterward, Jimenez de Quesada conquered what is now known as Colombia. Some years later, in 1558, the Spaniards located a mine at Muzo. The emeralds found there were breathtaking in both quality and size. The Spaniards promptly seized control of the mine and enslaved the local population using them to do the exhausting, dangerous work of digging out the gems. Within a few years, a veritable flood of big, almost flawless emeralds reached Europe, many of them finding their way into the hands of the Ottoman Turks, the Persian Shahs, and even the royalty of India. These stones were sculpted and engraved, becoming the foundation for many priceless jewel collections."-Awake! magazine February 22, 1999
Care instructions: Emeralds are brittle and sensitive to heat and pressure. Care must be taken to avoid knocks and scratches. Never use an ultrasonic or steam cleaner for your emerald! A soft toothbrush with a mild detergent is very effective.
Interesting fact: The "emerald cut" was developed for the sensitive nature of it’s namesake. Cut corners reduce the risk of the stone being chipped.
Emerald has been used for decorative purposes for thousands of years. They have beautified crown jewels and adorned some of the oldest royal dynasties. Emerald’s spellbinding color, unmatched by any other stone, accounts for its enduring appeal.
Mohs’ Hardness: 7 ½- 8
Specific Gravity: 2.67- 2.78
Chemical Composition: Al2Be3 (Si6O18) aluminum beryllium silicate
Refractive Index: 1.576-1.582
Crystal System: Hexagonal (trigonal); hexagonal prisms, columnar
Opal is the birthstone for October.
In the Orient, the opal symbolizes loyalty and hope. Arabs believed it came from heaven in flashes of lightning.
The name "opal" is derived from an Indian word for "stone", and what a stone it is!
The outstanding feature of opal is it’s opalescence, a rainbow-like iridescence which changes when viewed at different angles. The cause of this was theorized for decades, but finally discovered in the 1960’s under the 20,000x magnification of the electron microscope. Tiny spheres (.001 mm.) of a mineral called cristobalite (see "little known facts", below) layered in silica jelly cause the interference appearances.
Precious opal can be divided into several categories:
Hydrophane Opal- which becomes more transparent in water
Flash opal- Opal with sudden flashes of brilliant color
Black opal- Precious opal with dark gray, blue, or green background that accentuates color play
Milk opal- Opal with brilliant coloring on a white, milky background
Boulder opal- Opal that is naturally attached to the rock it was formed in, which is of a different chemical makeup
Opal matrix- Ironstone with thin veins or flecks of precious opal
Fire opal- Transparent opal of red or orange, showing no flashes of color, it is often facetted
The most valuable opals will have a fantastic play of color without "dead" spots or "crazing" (internal fractures). Large pieces of good quality opal command high prices. Very thin pieces of opal are sometimes cemented to a backing of common opal or black onyx, this is a "doublet". These are not as valuable as regular opals of the same size, though they can be just as beautiful viewed from the top. When the opal is even thinner, a clear top layer of quartz is added to the doublet, creating a "triplet".
Large deposits of opal are found in Australia. The staggering quantity mined there has completely eclipsed all other countries. Other places opal is mined: Brazil, China, Guatemala, Honduras, Hungary, Japan, and the U.S.
Care instructions: Opal is a medium to soft stone, so care should be taken to avoid scratching it. Never use abrasives to clean it, we had a customer who was actually told to polish her opal with Ajax! A soft toothbrush and mild soap work best. If your opal is set in a ring, take it off when you do rough work with your hands. Opal is sensitive to pressure, acids, alkalis, and heat. An opal can contain up to 30% water and high temperatures can evaporate the water.
Little known fact: Cristobalite is a mineral also found in lunar rocks, interesting...
No two opals are identical. It is an example of a soft gemstone which, because of its unparalleled beauty, has all the value of a much harder and more durable stone. The care it requires is certainly worth owning such a unique thing of beauty.
Mohs’ Hardness: 5 ½-6 ½
Specific Gravity: 1.98-2.2
Chemical Composition: SiO2..nH2O (silicon dioxide with a number of molecules of water)
Refractive Index: 1.435-1.455
SAPPHIRE & RUBY
Mineral name: Corundum
Only red corundum is called ruby. All other colors are considered sapphire. There is no definite color line where ruby ends and sapphire begins. If corundum is light red, pink or violet, it is usually called sapphire. If these colors were grouped as rubies, they would be viewed as inferior quality. In this way, they have individual values in comparison with the other colors of sapphire.
Ruby is the birthstone for July. It is named for its red color, Latin- Rubeus.
Rubies are rarer than sapphires, because the required pigment to make corundum red, chrome, is more rare than iron, the required pigment for sapphire.
Inclusions are common, and are not indicators of lower quality. The type of inclusion can often indicate source area. It is not possible to determine source area based solely on color.
Important deposits of ruby are found in Myanmar (Burma), Thailand, Sri Lanka, Madagascar, Afghanistan, Tajikistan, Malawi and Tanzania.
Ruby is one of the most expensive gems, large ones being rarer than diamonds of comparable size.
Sapphire is the birthstone for September.
Sapphires come in many colors; blue, pink, purple, orange, yellow, green, colorless(white), and black. Orange-pink is called Padparaschah, a Sinhalese word meaning "lotus flower". In fine quality, this is the most expensive of sapphires.
Large deposits are found in: Australia, Myanmar, (Burma), Thailand, and Sri Lanka. Some other sources are: Brazil, Cambodia, Kenya, Malawi, Tanzania, and Montana, USA.
Sapphire is consistently a favorite with both men and women, the most popular color is blue. Unlike many gems, sapphire comes in a wide range of colors, making it an excellent choice for jewelry.
Fact: Corundum, (sapphire and ruby) is considered a "9" on the Mohs’ scale of hardness. Only diamond, at "10", is harder. This can be a little misleading, however. Corundum is only 1/140th as hard as diamond! Topaz, which is "8", next in hardness, is only 1/7th as hard as corundum! Simply put, no other stones have come between these in hardness, so they are listed in numerical order, from 1 through 10.
Mohs’ Hardness: 9
Specific Gravity: 3.99-4.00 Sapphire; 3.97-4.05 Ruby
Chemical Composition: Al2O3 aluminum oxide
Refractive Index: 1.766-1.774
Crystal System: Hexagonal (trigonal); dipyramidal, barrel-shaped, tabloid-shaped
Tanzanite’s unique color, a bluish-purple, makes it easy to recognize. It has a beautiful brilliance and depth of color. Originally viewed as a substitute for sapphire, it has come into its own as a coveted gem.
History: It was discovered in the early1960’s in Tanzania, East Africa. Tiffany & Co. named the blue zoisite "tanzanite" after it’s discovery location, and began marketing it in 1970.
The only place tanzanite is found is in the Umba Valley, at the foot of Mount Kilimanjaro, in Tanzania.
The highest quality tanzanite is very deep in color, a good mix of blue and purple and without visible inclusions. Larger sizes are not very common, and thus command larger prices. Lower qualities tend to be very light in color.
Care instructions: Because tanzanite is medium in hardness, care should be taken to avoid scratching it. It can be cleaned with a soft toothbrush, warm water and a mild soap. Take care not to store it with other jewelry that can scratch it.
Fact: Tanzanite in it’s natural state, is most often an unattractive brown color. If you saw it lying on the ground, you probably wouldn’t be inclined to pick it up! Almost all tanzanite is heat treated (to temperatures of 752-932+ degrees F) to attain it’s stunning blue-purple color.
The owner of a fine tanzanite is very fortunate. Unlike many gems, tanzanite is found in only one place on earth. This in itself makes the gem a rare treasure. In addition, it displays beautiful brilliance and color.
Mohs’ Hardness: 6 ½ - 7
Specific Gravity: 3.35
Chemical Composition: Ca2Al3(O/OH/SiO4/Si2O7) calcium aluminum silicate
Refractive Index: 1.691-1.705
Crystal System: Orthorhombic; multi-faced prisms, mostly striated
Tourmaline is the birthstone for October.
It has a variety of rich colors greater than any other gem.
Important identifying features: High double refraction, or light entering the crystal and being divided two ways; and strong pleochroism, meaning the appearance of different colors when viewed from different directions.Tourmaline was first imported to Europe from Sri Lanka by the Dutch in the early 1700’s.
Tourmaline is often divided between "pink tourmaline" and "green tourmaline". However, tourmaline comes in nearly every color imaginable. Following are some varieties according to color:
Rubellite- dark pink to red
Indicolite- all shades of blue including blue-green
Dravite- yellow brown to dark brown
Verdelite- the most common tourmaline, green, in all shades
Schorl- black, very common, not valuable as a gem
Bi-color and tri-color tourmalines are also very interesting. These appear to be striped with distinct bands of color, typically pink and green or blue. Multi-colored tourmalines with an outer "skin" of green and a pink to red interior, are called "watermelon". When sliced and polished, that is exactly what they look like.
Large deposits are found in: Sri Lanka, Madagascar, Brazil, Nigeria and Mozambique. Also found in: Afghanistan, Australia, Canada, the island of Elba, India, Myanmar (Burma), Namibia, Nepal, Pakistan, Russia, Switzerland, Tanzania, Thailand, and the US.
The most desired colors are pink, intense red, “Windex” blue, blue-green and emerald green. It is of average hardness, so all the usual precautions apply, don’t use it to crack walnuts or knock on doors, don’t clean it with abrasives, store it away from things that can scratch. As with many gemstones, cleaning with a soft toothbrush and mild soap works very well.
Science experiment: Tourmaline can become electrically charged by heating and subsequent cooling. One end becomes negative, the other positive, attracting small particles of paper, ash or dust.
Unlike many gems, high quality tourmalines can still be found in very large sizes. Its extensive variety of colors, and reasonable price makes tourmaline a very desirable stone for jewelry.
Mohs’ Hardness: 7-7 ½
Specific Gravity: 3.02-3.26
Chemical Composition: (NaLiCa)(Fe11Mg Mn Al)3Al6((OH)4(BO3)3Si6O18) aluminium borate silicate, complicated and changeable composition
Refractive Index: 1.615-1.655
Crystal System: Hexagonal (trigonal);usually long crystals with triangular cross section and rounded sides, definite striation parallel to main axis, often several prisms grown together.