What Mineral is My Birthstone and what are its Properties?

Crystals and gemstones have been associated with months of the year for almost 2,000 years. Today, we call them birthstones.

Garnet – January’s Birthstone

January’s birthstone is Garnet. Garnets are often found in metamorphic rocks such as schist. Garnets are actually a family of minerals which are all similar. The garnets which are often used as gemstones are typically a dark red color; however, the brilliant green of variety of uvarovite is rare and very prized.

Amethyst – February’s Birthstone

Amethyst is a common, purple form of the mineral quartz.  Fairly hard, amethyst is a 7 on the Mohs hardness scale which has a range from 1 (softest) to 10 (hardest).  Crystals of the mineral often form in clusters, which are also called druze, and also commonly form in geodes.  The purple color of amethyst is due to the presence of ferric iron (Fe3+) in the quartz crystal and can range from light to dark.  When heated, amethyst will turn brown, into citrine.

Amethyst is considered a semi-precious gemstone that is most commonly used in jewelry and for collecting.  Beautiful samples of amethyst can be found in Brazil, Mexico, Uruguay, Russia, India, Sri Lanka, and the United States.

Aquamarine – March’s Birthstone

Aquamarine is a pale blue form of the mineral beryl.  Aquamarine crystals can occur in such rocks as granite and pegmatite.

These beautiful gemstones have a glassy luster (shine) and are either translucent or transparent.  These properties make aquamarine a prized stone for all types of jewelry.

Diamond – April’s Birthstone

Did you know that pencil lead and diamonds are made of the same thing?  It is hard to believe but they are both made of carbon!  The carbon forms in different crystal types or shapes, which is why they are different.  Diamond is the hardest mineral, being a 10 on the Mohs hardness scale.

Diamonds form in igneous rocks called Kimberlites and Lamproites. These igneous rocks are typically rich in the mineral olivine and derive from mantle rocks known as peridotites. The peridotite rocks melt deep below the surface (between 90 and 280 miles) of the Earth then rise through cracks in the surrounding rock forming pipe-shaped intrusions. As the magma pushes its way through the cracks, some of the surrounding rocks break off and mix into the liquid magma. Over time, (millions of years) the magma slowly cools into rock with large crystals. Sometimes these crystals include those wonderful gemstones we know as diamonds.  This photo shows cores of kimberlite rock from a drilling and exploration project. The rocks cores are stored these long, then boxes for examination. Geologists store the cores in order as they pull them from the ground so that they can view the rocks in one long string and see exactly what is present below the land surface.

The largest diamond ever found is over 7,000 carats which is about the size of your two fists put together.  Because of their beauty and strength, diamonds are used for a wide variety of products from jewelry to industrial cutting blades. The photo at the top left shows a group of different sized diamonds which have been cut and faceted.

Emerald – May’s Birthstone

Emerald is a green form of the mineral beryl.  Emerald is a hard gemstone that has a glassy luster (shine) and is either translucent or transparent.  The elements chromium and vanadium give emerald its green color.  Emeralds are one of the most rare and prized gemstones and can be worth more than diamonds if they are pure.

Pearl – June’s Birthstone

Pearls are a beautiful organic gemstone which is formed in a variety of colors and shapes.  Pearls form inside of mollusk shells such as oysters and mussels.  This unique gemstone is made of primarily the mineral aragonite.  Aragonite is the mineral that lines the inside of the mollusk shell.  An organic substance, called conchiolin, is also known to line the inside of the shell.  When shell linings are made of aragonite and conchiolin together, it is called mother-of-pearl.

To form the gemstone pearl, a grain of sand must get trapped inside the mollusk shell.  The aragonite forms in circles around the sand grain.  It can take between 2 and 8 years for a large pearl to be formed.  Fairly soft, pearls are a 3 on the Mohs hardness scale and have a white streak. The luster, “pearly,” is often used to describe the look of other minerals with similar outward appearance. Pearls can form in both freshwater and salt water and can be round and smooth to oblong and uneven.  Common colors of pearls include white, cream and black; however, other colors such as blue, yellow, gray, green, light purple and mauve can also be found.

Ruby – July’s Birthstone

Rubies are one of the hardest known minerals.  With a hardness of 9 on the Mohs scale, it is only softer than a diamond.  Rubies are known for their beautiful red color.  A ruby is a variety of the mineral corundum.  The gemstone sapphire is also a variety of corundum and comes in many colors, except for red.  Rubies have a glassy luster which makes them shiny.  Rubies are most commonly used for jewelry.  Rubies are commonly mined in Myanmar, Thailand, Kenya, the United States, Sri Lanka and Tanzania.  In 2005, a 440 carat ruby was discovered and thought to be one of the largest gems found to date.

Peridot – August’s Birthstone

Peridot (“pair-a-doe”) is the August birthstone.  This lovely green gemstone is a variety of the mineral olivine. Peridot gets its green color from the presence of iron in the crystal’s structure.  The amount of iron present determines the intensity of the green color such that the higher the iron content the darker the green color. Interestingly, peridot is only found in the color green whereas most other minerals can be found in more than one color.

Although olivine is common in igneous and metamorphic rocks, the gemstone quality version is much rarer. Arizona has one of the more abundant sources of peridot but the quality is not as high as in other regions, such as Egypt, Myanmar, Burma and Pakistan, which have smaller amounts of the gemstone. The Smithsonian Institution has a gemstone from Egypt that is over 310 carats, which is largest peridot ever found.

Sapphire – September’s Birthstone

Sapphires are a blue form of the mineral corundum.  When corundum is red, it is called a ruby.  Corundum is one of the hardest known minerals with a hardness of 9 on the Mohs scale.  The gemstone sapphire is usually known for its spectacular blue color, but can also come in many other colors, except for red.  Sapphires have a glassy luster which makes them shiny and are most commonly used for jewelry.  One of the largest sapphires in the world is called the “Logan Sapphire” and is over 422 carats.  Many beautiful specimens of sapphire are mined in Myanmar, Madagascar, Kashmire, and Sri Lanka, and Australia.

In the United States, sapphires and rubies can be found in the area of Franklin, North Carolina, which is a popular area for mines.

Opal – October’s Birthstone

Opal is a unique mineral because it forms as a gel in cracks of many different types of rocks. However, opal is most often found in rocks like basalt, rhyolite, sandstone and limonite.  High water content is a trademark of the opal.  Up to 20% of an opal can be water.  Opals come is a wide variety of colors including white, reds, greens, pinks, browns, and blues to name a few.  Most opals do not have a specific shape, however, “precious” opal which are used for jewelry do have a round structure to them. Almost all of the world’s opal supply comes from Australia.

Topaz – November’s Birthstone

The November birthstone is topaz.  Topaz is a unique gemstone which comes in a huge variety of colors such as orange-yellow, colorless, light blue, pink, brown and green.  Topaz has a hardness of 8 on the Mohs Hardness Scale and a glassy luster.  Igneous rocks are the most common type in which to find topaz gemstones.  Topaz is used for jewelry in its variety of colors.

Turquoise – December’s Birthstone

The December birthstone is Turquoise, a blue to green minerals which is moderately hard and typically shows no specific crystal structure. Turquoise is a 6 on the Mohs Hardness Scale of 1 to 10, has a pale blue to white streak, and a waxy luster. “Cryptocrystalline” is the term often used for minerals like turquoise where the crystals are so small that they cannot be seen.  Turquoise can be nicely polished and is therefore, used often in jewelry.

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Ask-a-Geologist #20: What can you tell me about the mineral pyrite?

Today I have a special guest with me. Her name is Piper and we are discussing the mineral pyrite.  (Make sure you watch the video until the end to see our first blooper reel!)

Piper: I got this pyrite sample as a gift. Can you tell me about it?

The mineral name “pyrite” is comes from the Greek word for fire. People believe that pyrite got its name because it will spark when you hit it with a steel hammer.

Pyrite is a mineral that is most often known as “fool’s gold” because it looks like real gold. Do you know how to tell the difference?

Piper:  No. How do you tell them apart?

They are both gold in color and are shiny and have a metallic luster, which is what the mineral looks like in the light. One of the best ways to tell pyrite from real gold is hardness. Gold is soft – about a 2.5 to 3 on the mohs hardness scale, while pyrite is much harder, a 6 to 6.5 on the hardness scale. You can scratch gold with a copper penny but you can’t scratch pyrite. Pyrite is also lighter weight than gold.

Now you might have noticed that your sample of pyrite has some really neat features. You can see a bunch of little crystals all growing together. Pyrite forms natural cubes and octahedrons which are shapes with four and eight sides. Sometimes it can form crystals with 12 sides too. Sometimes, you can see lines on the flat sides of the crystals too. Do you have any more questions about pyrite?

Piper: What can I use it for?

Well, some companies use pyrite to make sulfuric acid, but you don’t need any of that. A beautiful sample like this is best in a collection like yours.

Remember to keep your questions coming in through the dig into geology section on our website or email us at rockinfo@minimegeology.com.    Please comment below and subscribe to our channel so that you get the next installment of ask a geologist.    Until next time, rock on everybody.

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Glaciers are Awesome!

A glacier is a large, moving sheet of ice and snow.  Next to oceans, glaciers hold the most water on earth.  The polar areas are covered largely by glaciers and in warmer areas, glaciers cover the highest mountain tops.  Many other geologic features can also be formed by glaciers as well.  Glaciers can be found on every continent.

Glaciers typically move very slowly.  However, there are short times when the glacier moves faster than its normal speed.  Glaciers move rocks and soil as they move across the land surface.  Because of their shape, weight and the rocks they carry, glaciers can leave behind new geologic features as they travel.  Moraines form when rocks and other debris pile up on the sides and ends of a glacier.  Valleys, in the shape of a “U” are forms as a glacier passes over the land surface.  The study of glaciers is one of the most interesting subjects in geology.

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A Little Fun Info about Mountains!

A mountain is a tall mass of land that has been either formed through tectonic plate collision or stretching or by volcanic activity.  Mountains form some of the most spectacular and interesting scenery in the world.


Road cuts through mountains can expose angled rocks layers, folds and even metamorphism and volcanism which occurred during the episodes of mountain building.  Large mountains typically take many, many years to form.

Mount Everest (shown above), located on the border of Nepal and Tibet, is the mountain with the highest altitude in the world measuring 8,848 meters (29,028 feet) from sea level to the peak.

However, Mauna Kea (shown right) in Hawaii is the tallest mountain if you measure from the sea floor to the peak.   Mauna Kea is over 10,000 meters (over 33,000 feet) tall.

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Science Fun = Summer Learning (and the kids won’t even notice!)

During the summer we sometimes feel like our kids loose some the knowledge that they gained during the school year. I find myself constantly telling my kids to go read a book or work a few pages in their “thinking” workbook. But there are a few, not-so-quiet ways for kids to learn during the summer and they won’t even realize that they are finding out something new.

I designed the Mini Me Geology Rock Detectives line of kits to allow parents to give their kids a fun science kit that not only has large, nice rock and mineral specimens, but has a eBook full of information and ideas to keep your kids busy for hours, rather than in front of the television.

Each kit has 6 or 7  large mineral or rock samples (depending on which kit you purchase), custom hand lens with 3X and 6X magnifications and a 30 page, full color eBook on CD that includes mineral or rock information, sample identification activities, puzzles, coloring pages, experiments, an adventure story writing exercise for your young geology detective, and activities including making a personal geologist’s field notebook and your very own rock collection storage box.

Kids love these kits because of the unique shapes, colors and properties of the mineral and rocks and the activities and experiments in the eBook. The best part about these kits is that you can do the experiments with your kids so you can have a little science fun bonding time!

If you need a suggestion of which kit is best for your child, just shoot me an email and I’ll get right back to you. Click here to download samples of the Rock Detectives eBooks. Here is a little quick guide that might help you decide which kits your kids might love:

Mineral & Crystal Kits – have colorful mineral samples which unique properties, colors and shapes.
Igneous Rock Kit – has rocks made from volcanoes.
Sedimentary Rock Kit – has rocks made in rivers, oceans, lakes and deserts.
Metamorphic Rock Kit – has rocks that were buried way, down deep in the Earth and changed because of high temperatures, pressures and hot, hot liquids!

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