Sapphires are a member of the “corundum” family and refer to all colors of corundum except red. When corundum is red, we call it a ruby (see below). Sapphires are typically thought of as blue, but they can actually be almost any color including pink, yellow, and green. Fine blue sapphires are the most valuable and are highly desirable. Sapphires are very hard and durable, making them a great stone to use for jewelry. Most sapphires are heat treated to enhance their color - about 90% or more of all sapphires are heat treated. This treatment is stable, permanent, and when disclosed to the buyer, perfectly acceptable.
Rubies are also a member of the “corundum” family and refer to all stones of this family that are red. The most desirable shade of ruby is called “pigeon’s blood”, which is pure red with just a hint of blue. An exceptional ruby that is very large is rare, and will often times be more expensive than a diamond. Like sapphires, rubies are very hard and durable, making them an excellent choice to wear in jewelry. It is also common for rubies to be heat treated to enhance their color. This treatment is stable, permanent, and when disclosed to the buyer, perfectly acceptable.
Emeralds are the most precious stone in the “beryl” family. The green color of emeralds is due to the presence of chrome in its chemical structure. Highly transparent, rich green emeralds are extremely rare and expensive. Emeralds are typically highly included (internally flawed) and only the very finest examples are transparent. Inclusions are not seen as faults in emeralds since the majority of stones are clouded this way. It is very common for most emeralds to be oiled in some way to hide fractures, and when disclosed to the buyer it is perfectly acceptable. However, oiling treatments are not very stable and care should be taken to keep the stones away from heat and ultrasonic jewelry cleaners. Emeralds are also a fairly soft stone, and they are much more highly prone to scratches and breakage. If emeralds are cared for and worn properly, they will last several lifetimes.
Tourmalines are typically seen in green and pink. Many people don’t realize though that they can come in almost any color you can imagine and one gemstone can have more than one color as well. “Watermelon” tourmaline occurs when a ring of green tourmaline forms around a center core of pink tourmaline like a slice of watermelon. Tourmalines are mined mainly in Brazil, Africa and the United States. One of the main deposits in the U.S. is the Himalaya Mine in San Diego county known for its bright pink tourmalines. An interesting property of tourmaline is that it can become electrically charged when heated and then cooled and by applying pressure such as rubbing it on a surface. The stone will then attract dust and other particles. This effect is called pyro-electricity and because of this tourmalines should be cleaned more often than other gemstones. Heating tourmaline can sometimes change or enhance the color of the stone but this treatment is not always permanent.
Jade is most often thought of as a green mineral but can occur in a wide variety of colors including brown and lavender. Its value lies in its beauty and is judged by its color, texture, translucency and size. If there are multiple pieces of jade in an item of jewelry then how well the jade is matched is also part of determining value. Imperial jade is the most coveted type of jade and is a rich emerald green color that is translucent to almost transparent. It is important to note that a majority of jade available today has undergone some form of treatment such as dying or heating to improve its color.
Amethyst is the most highly valued gemstone in the quartz family. It ranges in color from a light lavender called “Rose de France” to a deep rich purple. It can also have a tinge of blue or red to its overall color as well. The word amethyst comes from ancient Greek and means “not drunken” since it is thought that wearing amethyst will protect the wearer from drunkenness. Amethyst has been used in jewelry throughout the centuries by the Egyptians, Greeks and medieval Europeans to name a few. It has also been a favorite gemstone of the Christian church and many amethysts have been used in religious jewelry. The most notable locations for amethyst are in Brazil, Madagascar, Russia and the United States. The Four Peaks mine in Arizona has produced highly desirable deep royal purple amethyst with a hint of red. Heating amethyst can change its color to green. These green quartz stones are called Prasiolite.
Citrine is a yellow or golden variety of the quartz family. Naturally colored citrine is a very light yellow and are very rare. Most citrine is actually light colored amethyst or smoky quartz that has been heated to bring out a rich yellow color. This heat treatment is completely stable and accepted in the jewelry industry. Natural color citrine is mined in many different countries including Brazil, Madagascar and the United States.
Opal is different and not technically considered a mineral because it is primarily made up of anywhere between 3% and 30% water. Opals are extremely fragile because of this water content and those with lower water content have better chances of not breaking. Most opals have what’s called play of color meaning the rainbow colors that flash when an opal catches the light. This play of color occurs because of the way the silica spheres are stacked in an orderly fashion on top of each other. 97% of the worlds opal supply comes from Australia but it’s also found in the United States, South America and Eastern Europe among others.
Coral belongs to a small group of organic gemstones. The coral that is used in jewelry is formed by small ocean organisms into branch like structures that range in color from a deep “ox blood” red to an orangey salmon color to a very pale “angel skin” pink. Deposits of coral can be found in the western Mediterranean coastal waters and in Japan and Hawaii among others. Coral reefs are diminishing worldwide however and production has been limited due to environmental restrictions. Coral has been used by the Romans, Greeks, Chinese and Native Americans as well as others throughout history as a form of adornment. Some coral is treated with dye in order to deepen or change the color and increase desirability. This dye may fade over time and is not always permanent.
Turquoise means “Turkish Stone” because it entered Europe via a trade route through Turkey. It is an opaque stone that is bluish-green and commonly includes spots or veins of the host rock material called matrix. Turquoise that does not contain any matrix is highly prized and can be extremely valuable. Turquoise is relatively soft and can scratch easily. It’s also porous and can be discolored by oils from skin or lotions. Because it is porous it is often treated with fillers like wax or resin to fill fissures and to stabilize the color. Turquoise is one of the oldest documented minerals to date. Ancient Egyptians, the Aztecs, Persian and Mesopotamia society and even ancient China all mined and used turquoise for adornment. There are many mines for turquoise in the United States, Arizona being the most important producer. The most famous mine in Arizona is the Sleeping Beauty mine in Globe, AZ. The finest and most highly prized turquoise however is Persian turquoise with an intense blue “robins egg” color that is free of any matrix.