So much to cover here! To start with, gemstones are rated on their hardness, landing on a scale from one to ten (the Mohs Hardness Scale). The hardest stone can scratch every other stone, and that rating belongs only to a diamond. 

Merriam-Webster dictionary defines a gemstone as: "a mineral or petrified material that when cut and polished can be used in jewelry." This encompasses a pretty wide range of materials, including crystals, fossils and even meteorites!

Gemstones have many classifications, from measurable attributes (such as carat weight, clarity, color and cut - the 4 C's), gemological attributes (such as the way they reflect or refract light and the way they break), to metaphysical attributes such as associated meanings and healing properties. 

Below is a list of gemstones with a little information about each. I hve tried to include some fun facts about each stone. This is an abbreviated list, let me know if you want information on something you don't see here:

Alexandrite is the most expensive gemstone in the world. Per carat, it can be more expensive than a diamond. Why? Rarity, of course, plus it's magical color-change abilities. In daylight, it appears pretty emerald green. Under fluorescent lighting, it turns purplish-red.

Alexandrite is birthstone for June, along with pearl and moonstone. Alexandrite is also the gem for the 55th wedding anniversary.

Amazonite is named for the Amazon river in South America. It was not named for the region in which it is mined, but rather to bring to mind the jungle greens and watery blues of the region. It was actually used quite a bit in ancient Egypt. 

This is another feldspar mineral, along with labradorite and moonstone. Feldspar makes up the majority of the earth's crust, but only some of it develops with the right conditions to make gemstones.

Amazonite is a soothing stone. It helps you see both sides of a problem or different points of view. It is also sometimes carried for good luck when gambling.

Amber is fossilized resin from ancient trees, and the oldest specimen has been dated to 320 million years old! Technically not a stone, it's considered a gem material. As it solidifies, it traps things in it, from pieces of bark and leaves to intact insects and even a dinosaur feather. Scientists have actually tried to extract DNA from some of these creatures, à la Jurassic Park. So far, no luck, but they are apparently still trying!

Amethyst, the purple variety of quartz, is also the most expensive variety.

The name comes from the Ancient Greek amethystos, which means "not drunk," and was therefore thought to prevent intoxication. 

A beautiful pale lilac colored type of amethyst is called Rose de France.

It's the birthstone for February and the anniversary stone for 6th and 17th years.

Apatite is named for the Greek for "deceit," because it has been confused with many other stones, including the very expensive Paraiba tourmaline.

This relatively soft stone generally has a blue-green translucent appearance. It contains the same mineral makeup as human teeth and bones, and it has also been found in rocks collected from the moon.

Because it is chemically similar to animal teeth and bones, it is favored in jewelry by animal conservationists. Metaphysically, it is used in bone and joint health.

Aquamarine is a beryl, the same family as emerald. Named for the Latin for seawater (obviously), the stone was thought to calm rough seas.

It is the birthstone for March and an anniversary stone for the 19th year of marriage.

Like the stone itself, the name Chrysocolla is an aggregate: named in 500 BC, its name is the Greek for gold (chrysos) and for glue (kolla) as it looks like the flux used to solder gold in ancient times.

Citrine is the golden yellow variety of quartz crystal. It's actually a heated version (either by man or nature) of amethyst. Ametrine is a partially evolved citrine and is half purple, half yellow. A hard stone, it can withstand some abuse, it is easy to find in nearly flawless quality with few to no inclusions, and can be cut in a variety of styles.

Obviously, the name comes from its color, reminiscent of citrus fruit, but citrine is available in all the shades of yellow, from pale Lemon Citrine to deep Cognac Citrine.

Citrine is warm yellow and is therefore associated with sunshine and happiness. It is the birthstone for November and commemorates the thirteenth anniversary.

Diamonds, the "gold standard" of gemstones!

It is the only gem that rates a ten on the Mohs Hardness scale, as it can scratch every other gemstone and none other can scratch it. That's why people sometimes check the authenticity of their stone by pressing it and dragging along glass. 

It is made of only one element - carbon. It's essentially coal that has been put under intense heat and pressure for about a billion years. 

Diamonds are valued most when they are colorless, but diamonds can be found in many colors, deemed "fancy diamonds."

The idea that a diamond must be given as an engagement present is actually the result of a successful marketing campaign by De Beers, a diamond mining company, in the 1940's. Prior to that, diamonds were rarely given as tokens of love.

Did you know: a star has been discovered 50 light years away that appears to be made of diamonds, with a total carat weight exceeding ten billion trillion trillion carats. Scientists have named it Lucy for the Beatles song Lucy in the Sky with Diamonds.

Diamond is the birthstone for April.

Emerald is in the same family as aquamarine. What sets them apart is the iron content that makes aquamarine blue and the chromium that gives emerald its distinctive coloring.

Emerald is one of those stones where absolute clarity is so rare that you generally want to see inclusions or else you might question its authenticity.

The oldest emeralds have been dated to three billion years old!

There is a myth that if you give someone an emerald as a token of love, it will change color if they are unfaithful.

It is the birthstone for May and commemorates the 20th and the 35th anniversary.

Iolite is a deep blue-grey, leaning towards purple in the right light. Its name comes from "ios," the greek for violet. It is a pleochroic stone, meaning that when you look through it and change the angle, the color changes. This feature was helpful to Vikings, who used it like polarized sunglasses to help them navigate the seas.

Jade is that translucent green stone so often seen in small sculptures, but it was originally used, over 5,000 years ago, to make weapons such as axe heads because it is lightweight and very tough.

Jade actually occurs in many colors, but one clear green variety called Imperial Jade is considered by some to be the most expensive gemstone in the world.

Jade is considered lucky when given as a gift, and very unlucky if you steal it! 

It is the stone for 12th anniversaries.

Deep blue and streaky in appearance, Kyanite gets its name from the ancient greek for blue (kyanos). Recognize the word? Your printer's cyan cartridge is named for the same word. The color is so striking, it has been referred to as the "poor man's sapphire." 

Kyanite is anisotropic, meaning it can be strong under pressure in one direction and more brittle in another. This gives it two separate ratings on the Moh's Hardness scale and requires a gentle treatment.

Labradorite is actually a feldspar, a type of mineral that makes up the majority of the earth's crust. But with this stone, it develops in layers that absorb some light wavelengths and reflect others back. So you end up with this rainbow light effect called labradorescence (yes, that's the name). Without light, it usually appears grey. In this stone, you expect to see inclusions, or growths inside the stone. A visually clear stone won't have much light dispersion (= less fun) Labradorite is not a birthstone, but sources say that it represents the Vernal Equinox (Feb 19 - March 19) and heralds the coming of spring. Original mined in Labrador, Canada, its light play has been compared to the Northern Lights and that's why some call it the Aurora Borealis stone.

Lapis means "stone" in Latin - as in lapidary, while Lazuli means blue. Pretty basic etymology there. This opaque, deeply blue stone is often found with shiny flecks of pyrite in it (as in iron pyrite, also known as fool's gold). 

The blue is so intense, it is often ground up into pigment powder to create the color ultramarine. This pigment was used in Van Gogh's Starry Night and by Michelangelo to paint the ceiling of the Cistine Chapel. Lapis is the stone used for the eyes in King Tut's death mask, but Egyptians also used the powder for cosmetics! Many ancient civilizations used Lapis for practical as well as decorative purposes.

This is the stone used to represent the ninth anniversary.

Larimar is a mottled blue and white gemstone discovered in 1974, and found only in the Dominican Republic. It is named for "mar" for the sea, and "Lari" for Larissa, the daughter of one of the men who discovered it. The appearance of this stone mimics the play of light on a surface under water in the sunlight. Ironically, sunlight can fade the blue coloring, which comes from copper.

Malachite is a forest green, opaque stone has a coloring that comes from copper and an appearance that includes bands of varying shades of green.

A relatively soft stone, it is often carved into ornamental objects and because it is a common stone, it is sometimes found in architectural elements such as columns and even wall trim.

Malachite is considered a "protective" stone that can help ward off evil spirits.

Moonstone gets its name from the ethereal glow it gives off, a result of the layers it develops during formation. This effect is called adularescence. 

Moonstone actually comes in many colors, it's the light effect that determines its classification, which is in the feldspar group, the most common stone in the world, making up 60 percent of the earth's crust. Rainbow moonstone with its oily, multicolor refraction, is actually a form of labradorite, while true moonstone stands alone with its blue shimmer.

Moonstone is a birthstone for June, along with pearls and alexandrite. It represents anniversaries for the 13th year and every 13th years thereafter. Lucky moonstone!

There are so many types of Opal: solid black opal, translucent Welo opal, boulder opal, fire opal, Peruvian opal... and each has its own characteristics. 

Precious opal encompasses the types that have "opalescence" - that famous play of color that adds the most value. A piece with the best color play can sell for over $10,000 per carat. Most times, these types are made into thin slices and then affixed to an ironstone backing (that's the plain brown or black mineral that is often mined along with precious opal). Even these thin slices can appear to have real depth but are much more affordable than a solid piece of opal.

Common opal lacks that play of color, but can also be lovely, as with Peruvian opal, which has a stunning oceanic blue-green color.

All opal contain water, which means that they can dry out and crack if not cared for properly. In fact, their reputation as unlucky comes from buyers whose stones have cracked as a result of drying out. 

Please note that doublets and triplets, as I use in most of my jewelry, are not affected by this, only solid pieces of opal should be routinely exposed to water.

Egyptians called Peridot the “gem of the sun,” probably due to it's fiery yellow-green coloring, which comes from iron. It's also the only interstellar gem to be discovered - this gem has been found on pallasites, special meteorites containing the stone.

Peridot is a birthstone for the month of August. It's the stone that represents a 15th anniversary.

Prasiolite is the pale green variety of amethyst.  It's pretty easy to find eye-clean prasiolite. It gets its name from the greek for "leek," and is named for its color (source: Wikipedia). 

Rose quartz is the pink variety of crystal quartz. Mineral inclusions cause the color to be slightly cloudy. 

It is believed to be the stone of love and commemorates fifth anniversaries.

Ruby is the red variety of corundum. All other colors of corundum are called sapphire. It rates as a 9 on the hardness scale, just under diamonds.

Ruby gets its coloring from chromium, which is very rare in gems. This rarity gives rubies a value above most sapphire.

I used to believe that Rutilated Quartz was a stone that had gone through a process of "rutilation." No such term exists. Actually, it is clear quartz crystal with inclusions of rutile, which develops in needle or hairlike patterns within the quartz, making each stone completely unique.

These inclusions can vary from pale brown to rich gold. If they appear black, you may have a piece of tourmalated quartz on your hands (that's tourmaline).

Sapphire's name comes from "sáppheiros," the Ancient Greek for "blue stone," which is interesting because sapphires run the widest range of colors of any gemstone, including white and black. Every color other than blue or red is called "fancy" sapphire. Blue is just called sapphire... red is called ruby! 

This stone is in the corundum family, second in hardness only to diamonds.

Sapphire is the birthstone for September.

Smoky quartz has naturally irradiated aluminum in it (radiation from the sun). All quartz stones have the same properties but the color varies depending on what mineral is around it. This includes amethyst, citrine, rose quartz and crystal quartz.

Smoky quartz is the National Gem of Scotland and the official State Gem for New Hampshire. 

Sodalite, the deep blue mineral with cobbled streaks first found in Greenland, it gets its color from sodium content, and that's also where it gets its name. 

Often rarity is a consideration of value, yet Sodalite remain generally affordable despite the fact that it is a relatively rare stone, mined in only a few locations worldwide.

Sometimes called "The Wisdom Stone," it is thought to enhance intuition and help you navigate through rough waters in life.

Spinel is a hard stone, similar to topaz, and that makes it expensive. It comes in many colors, but is most famous for the red variety, which so much resembles ruby that it was discovered that the Royal Crown of England's famous center ruby is actually a spinel!

Black spinel is called Pleonast, but has nothing to do with the literary term, which means "one who uses more words than necessary."

Spinel is an accepted birthstone for August, along with peridot.

Tiger's Eye forms in a way similar to fossils. Quartz develops over a mineral called crocidolite, a fibrous mineral similar to asbestos. The crocidolite dissolves under the pressure, leaving only the quartz with a silky chatoyant (cat's eye) effect and a golden coloring. With fossils, minerals seep into organic material and eventually replace them, leaving, basically, a stone with the look of the original material. 

Tiger's Eye has been used as a protectant against dark magic.

Topaz: In Sanskrit, "tapas" means fire, as in the fiery appearance seen when this stone is cut, and this may be where topaz gets its name.

Topaz is a stone that rates an 8 on the Mohs Hardness Scale, and is valuable in its many colors. Blue topaz is often irradiated in a lab to create the intense blue hues of Sky Blue, Swiss Blue, and London Blue topaz. 

The largest faceted gemstone in the world is the ‘El Dorado Topaz,’ which weighs in at  31,000 carats.

Tourmaline's range of colors is second only to sapphire. Black is actually the most common color, and the most famous is "watermelon tourmaline," which develops a green outer region with a pink center! 

The most expensive variety is called Paraiba tourmaline from Brazil, which utilizes copper for its blazingly vivid teal color (wish I could afford some).

This gemstone grows like a 3-sided crystal (unique to tourmaline), to and can become electrically charged when heated or squeezed!

Tourmaline is October's birthstone and the eight anniversary stone.

The best Turquoise is a rich, robin's egg blue. The veins in most varieties are made from copper (the blue in most gemstones comes from copper and turquoise is no exception). The veining through a stone is called the stone's matrix.

The finest turquoise in the United States comes from the Sleeping Beauty mine in Arizona, which produced clean blue stones with little veining. The mine was named for the shape of the mountain over the mine, which resembles a sleeping woman. However, it is so expensive to mine for the gems that they stopped mining for turquoise and now mine only copper there, making true turquoise from that area even more valuable.

Turquoise is the birthstone for December and represents the 11th anniversary.

Most people think of Zircon as cubic zirconia, an inexpensive substitute for a diamond. However, cubic zirconia is made in a lab and is not the same as the gemstone zircon, which has a fire that rivals diamonds in a natural stone. Zircon is available in a range of colors.

Zircon displays pleochroism; when viewed at different angles, it can appear different colors!

A piece of zircon was carbon dated to be 4.4 billion years old, making it possibly the oldest dated thing on earth! It appears in the Bible and in ancient Hindu poetry. 

Zircon is a birthstone for December.