Amethyst
One of the most popular of all gemstones is Amethyst. The purple quartz ranges from pale lavender to a deep purple. The more transparent this gem is, the higher the quality.
Amethyst is abundant, and therefore is not as expensive as other gems.
The hardness rating is 7.
Amethyst is the birthstone for February.

Aquamarine
If left out in the sun, Aquamarine can become paler. The highest quality is transparent. The colours of Aquamarine range from light blue, to blue green and dark blue.
The hardness rating is 7.5
The two birthstones for March are aquamarine and bloodstone.

Citrine
Citrine can occur naturally or can be produced when you heat amethyst under controlled conditions. Citrine varies in colour from light yellow to a rich golden yellow colour all the way to a dark orange.
The darker the colour, the more sought after!
Two gems are appropriate for November birthdays - Topaz and Citrine.

Diamonds
Diamonds are a girls’ best friend!
The colour range for a diamond is pale yellow to no colour at all, which are the most prized.
Having said that though, the much rarer and more expensive diamonds are brightly coloured. The Smithsonian collection has the Hope Diamond and the Eugenie Diamond, both being a deep blue colour are 2 of the most famous examples.
The hardness rating of a diamond is a 10!
The birthstone for  April is the diamond.

Emeralds
The stunning green comes from Chromium and vanadium. Emeralds range from medium to dark in colour.
Most emeralds are flawed by small inclusions and fractures. This makes the emerald more fragile. Many of these stones are impregnated with oils and waxes to both mask these flaws and enhance the colour.
The hardness rating for an emerald is 7.5
The birthstone for May is the emerald.

Garnets
If a garnet is cut to be larger than 2 carats, it appears as black, so normally garnets are cut to smaller sizes and will show their dark brown to purplish red colour better.
They can range from colourless to black which surprises those who think of garnets as being red.
They have a hardness rating of 7.5.
Garnet, the birthstone for January, signifies eternal friendship and trust and is the perfect gift for a friend. 

Jade
Jade has two types. Jadeite and Nephrite.
Of the two, Jadeite is a rarer and higher quality, it is known as imperial Jade.
It comes in many colours. Red, yellow, green, lilac, black, orange, white, pink, blue and brown.
The hardness rating of Jadeite is 7.
Nephrite Jade is the more common type and is often used in Chinese carvings. The colour is an olive tone.
It is a bit softer, with a hardness rating of 6.5.

Opal
A large opal is rare, and expensive! There is normally a play of colour in the opal that determines the value of the stone.
On the Mohs’ scale, the scratch hardness of an opal is between 6.0 and 6.5.3
October is another month with two birthstone choices – Tourmaline and Opal.

Pearls
The pearl is formed in shellfish, beginning as an irritant, such as a grain of sand.
A cultured pearl is created by adding a piece of mussel or shell inside of an oyster or mussel. As layers grow over the piece from the inside of the shell, a pearl is formed!
Prices vary depending on factors such as luster, size, colour and type as well as how the pearl was grown.
The more expensive being the natural pearl, then the cultured pearl, followed by the much less expensive fresh water pearl.
The colour range is from white, brown, silver, cream, black or pink. Colour is dependent on the type of shellfish and the water.
The hardness factor of a pearl is 3.
June counts three gems as birthstones, pearl, Alexandrite, and moonstone.

Ruby
The red colour of the ruby will vary as it is dependent on the chromium and iron content in the stone.
The ruby is quite hard and durable, but can still be chipped or fractured if handled roughly.  The ruby is found all over the world. The bright red rubies are mined in Afghanistan, Pakistan and Vietnam. The darker rubies are from Thailand, while the darkest are from Australia, India and Russia. These dark stones are also found in Georgia, North Carolina and Wyoming.
The birthstone for July is the Ruby.

Peridot
Peridot is a gemstone that forms deep inside the Earth and brought to the surface by volcanoes. Today, most of the peridot supply comes from Arizona; other sources are China, Myanmar, and Pakistan.  This gemstone comes in several color variations ranging from yellowish green to brown, but most consumers are attracted to the bright lime greens and olive greens.  Peridot, in smaller sizes, often is used in beaded necklaces and bracelets.
Two birthstones are available for August birthdays: Peridot and Sardonyx.

Sapphire
Most people think of sapphires as being blue, however, they can come in a variety of colours, such as orange, yellow, violet, green, white and pink. Some will actually change between blue and violet depending on the lighting. Sapphires are quiet hard, but will still fracture and chip.
The hardness factor of a sapphire is 9.
The birthstone for September is the Sapphire.

Topaz
The topaz can be blue, yellow, pink, brown, green or clear. The rarest colour is orangish red, which is the Imperial Topaz.
The hardness factor of topaz is 8.
Two gems are appropriate for November birthdays - Topaz and Citrine