Optical Calcite
Optical Calcite is a transparent form of Calcite which is, chemically speaking, Calcium Carbonate. Commonly called Iceland Spar thanks to Iceland's prolific output of this crystal, this form of Calcite is eye-catching for its perfect rhombohedra cleavage and demonstration of birefringence or double refraction. Light travels through Optical Calcite in two different directions and with two different velocities (one fast, one slow) which produce two different light rays. Observe this effect

by placing a piece of paper with writing on it underneath Optical Calcite to see two images slightly offset from each other.
It is speculated that Vikings used this light=polarizing property of Optical Calcite for navigational purposes, to tell the direction of the sun on cloudy days. Scientists in the late 1600's marveled at the properties of Optical Calcite which kick-started discoveries that would make major contributions to crystallography and optics during the next three centuries. Today, Optical Calcite is used in technology to provide high purity linear polarization for broad-band sources or multiple laser wavelengths (when you shine a laser into it, the beam splits into two).
Metaphysically, Calcite promotes macrocosmic awareness and reverence of the creative forces of nature. It is a powerful energy amplifier useful in multi-directional energy distribution. It calls forth a spectrum of energy to clear and activate the chakras and etheric field. Try it as a meditation ally.
Calcite is associated with the power of our minds and the body related with memory. A great ally for channelers and astral travelers, Calcite helps us to recall the information we receive on other levels of existence. Befriend Calcite to help your body remember the natural state of perfection in order to return to it when healing.
Optical Calcite reminds us of the double meaning of words and thus helps when communication is difficult. Energetically it can be used to promote the de-calcification of bone growths and balancing the assimilation of calcium within the body. It is a powerful detoxifier of the physical as well as the energetic body. I recommend that you cleanse your Calcite crystals regularly, but note that sea-salt solutions are not the best option as Calcite is so soft.
Consulting Optical Calcite for clues in my research, I was led to have found that Calcite is present within the human body in two interesting places, the otoconia structure in the inner ear and the pineal gland in the approximate center of the brain. Calcite exhibits piezoelectricity, meaning an electrical field is created when pressure is applied. A vibration, such as sound, can be converted into a corresponding electrical signal. Sacred temples or chambers all over the world appear to be designed intentionally as sound resonators with proportions calibrated specifically to the human vocal range. I suspect the piezoelectric calcite and quartz content of the stones may have been used to resonate the calcite biomineralizations of the pineal gland, which could possibly induce a hemispheric synchronization in the brain...among other interesting effects.
Check out our Optical Calcite available in our online shop.