How to Identify and Select Crystals Part Two: Optical Properties- Transparency
The first part of our series looked at how we could use color to help identify our crystals as well as how color can help us learn the metaphysical properties of crystals. This week, we will focus on optical properties other than color to help us identify crystals. By shining light on our unidentified crystals and stones we can narrow down what exactly we are looking at. This method reigns especially true when it comes to the dozens of different Jaspers and Agates available!
An easy tool we can use in our identification efforts is transparency. There are three ways to describe how light passes through a mineral. They can either be transparent or semi-transparent, translucent or opaque. For a crystal to be considered transparent, light must pass through it completely. (Since most crystals and stones commercially available are not gem quality, meaning they are not 100% without impurities, semi-transparent crystals are more commonly available.) Any object on the other side of the crystal are seen clearly. For example, take a clear quartz crystal or tumbled stone and place it on a piece of paper. Shine light directly on the crystal and see if you can read the text on the other side. In my example below, you can perfectly read the text through the Quartz Crystal. This demonstrates perfect transparency.
Since most of the crystals and stones available at crystal shops are not considered gem quality, meaning they are not without impurities, amongst other factors, we should know that some of our crystals will be semi-transparent. Look at the example below of a piece of Fluorite that I am in the process of cutting and polishing below. Notice there is an obvious impurity on the top right side of the piece pictured. Because of this impurity light cannot pass through in the same way as it does in the rest of the piece. We would call this crystal an example of being semi-transparent.
Translucent Next we have translucent crystals. Translucent crystals allow some light to pass through them, but objects behind the crystal may be hazy or unclear. A great example of a translucent crystal is the Agate I photographed while facing the bright morning sun. We can see the light passing through the Agate along with the details within the Agate's structure, but if we tried to read something behind it, we would have a blurry or obscured view.
Lastly, there are minerals and crystals that do not allow any light to pass through. These are referred to as opaque. When a crystal is opaque you can hold it up to the brightest of lights and not see anything through it. An example of an opaque crystal is the picture below of a Tigers Eye heart. Notice how we cannot see any light passing through the stone despite the picture being taken at the same times as the Agate above.
How can this help?
When you are struggling to identify one of your crystals or tumbled stones shine a light behind it to check its level of transparency. This technique is especially helpful when you are uncertain if you have an Agate or a Jasper. Both Agate and Jasper are varieties of Chalcedony, a microcrystalline or cryptocrystalline variety of Quartz. This means they have the same internal crystal structure as Quartz, but their crystals are so tiny we can only see them with a really good microscope.
Microcrystalline Quartz in its pure form should be semi-transparent. However, when a small amount of impurities or foreign materials are included, the color of the microcrystalline quartz changes and so does its ability to transmit light. Jaspers contain enough impurities and foreign material to make them opaque. So basically the only difference between a jasper and an agate is the amount of impurities and foreign material within the specimen as it was forming in the Earth!
Stay tuned for our next post that explores Optical Properties such as Labradorescence!!!
Sandra and Nicole
Soul Sisters Designs
Farndon, John, and Alec Livingstone. The Practical Encyclopedia of Rocks and Minerals: How to Find, Identify and Collect the World's Most Fascinating Specimens, Featuring over 800 Colour Photographs and Artworks. N.p.: Lorenz, 2008. Print.
"What Are Agate, Jasper and Chalcedony?" Rock Tumblers. N.p., n.d. Web. Retrieved on October 7, 2017 from https://rocktumbler.com/blog/what-is-agate-jasper-chalcedony/