adventures in museum-going

tourmaline (primary object)

tourmaline_whole

Primary Object Description

Scientific name: Cyclosilicate Mineral Tourmaline
Catalog #: 80475
Collected from: Oxford County, Maine, United States, North America

Our primary object is a specimen at the Q?rius Learning Center at the Smithsonian National Museum of Natural History (NMNH) in Washington, D.C. Tourmaline (scientific name: cyclosilicate mineral tourmaline) is a crystal encompassed by rock. Our specimen has multiple crystals in a metamorphic matrix (rock) which is approximately 7cm long, 5cm wide and 4cm tall. This specimen is approximately the size of a small apple. Our object feels heavy and dense when held, compared to pumice, an igneous rock that is very light.

The tourmaline crystals are grooved and elongated, and have a triangular cross-section. In geologic terms, the crystal structure is trigonal (pdf). The crystals are smooth to the touch, but under a microscope, they appear to be striated. In natural light, the crystals are a dark brown/blackish color. However, when under direct light, the surface reflects golden yellow. The matrix surrounding the tourmaline crystals is jagged and rough, and sometimes interrupts the crystal structure. It is a myriad of colors: yellow, pale green, brown, amber, white, shades of grey, and flecks of metallic gold.

tourmaline_micro_reflection

History

According to the Smithsonian Institution’s National Museum of Natural History, “The name tourmaline comes from the Sinhalese word turmali, used by Sri Lankan merchants to describe an undetermined mix of gemstones.”

Tourmaline is known for both its affordability and its spectrum of colors. Bi-colored and multicolored crystals are also common. These fine-cut gems are often set into jewelry. Industrial uses for tourmaline include use in high-pressure gauges to measure explosions and in gas-grill igniters, due to its piezoelectric property, in which a substance becomes electrically charged under pressure. Tourmaline is also used to coat internal elements in hair dryers. It is considered by some to have metaphysical properties, such as the ability to reduce stress.

Tourmaline crystals are most commonly found in igneous rock, and may rarely be found in metamorphic rock, as in our object. Metamorphic rock is formed under the extreme pressures and temperatures of the Earth’s geologic processes, which cause the rocks’ crystalline form to physically and chemically change. The resulting rock is more dense than in its original form and less subject to erosion.

The Big Idea
Formed over millions of years through constant stress of the Earth’s weight and high temperatures, our specimen exemplifies the change pressure can cause. Stress, both literally and metaphorically, comes in many forms and affects people and objects in a variety of ways. Whether these stresses are negative or positive, large or small, the end result is something new. Stress creates change.

References

Crystallography. (n.d.). Crystallography. Retrieved January 14, 2014, from http://webmineral.com/crystall.shtml

Live Webcast Jan. 16: Join Us for Fossil Whales!. (n.d.). Q?rius. Retrieved January 14, 2014, from http://qrius.si.edu


Piezoelectric Effect. (n.d.). Piezoelectricity. Retrieved January 13, 2014, from http://hyperphysics.phy-astr.gsu.edu/hbase/solids/piezo.html

Matrix (geology). (n.d.). Encyclopedia Britannica Online. Retrieved January 14, 2014, from http://www.britannica.com/EBchecked/topic/369508/matrix

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