Labradorite is a member of the feldspar mineral family, which makes up a significant portion of the Earth’s crust. It is best known for its striking internal iridescence, an optical effect termed labradorescence. Light interacting with the stone’s internal structure produces a shifting, metallic sheen of brilliant colors, often appearing as flashes of blue, green, gold, and sometimes red. This unique visual phenomenon makes labradorite highly sought after by mineral collectors and jewelers.
Global Geological Origins
The search for labradorite begins in the ancient geological formations where it was first discovered on Paul’s Island near Nain in Labrador, Canada, which is the source of its name. The mineral is predominantly found in intrusive igneous rocks that have cooled slowly beneath the Earth’s surface. Specifically, it forms within anorthosite, a type of rock almost entirely composed of plagioclase feldspar. These anorthosite massifs represent some of the oldest and most extensive rock bodies on the planet.
Beyond its namesake location, significant deposits are sourced from other regions worldwide. Finland is renowned for producing a variety known as spectrolite, distinguished by its particularly vibrant, full-spectrum play of colors. Gray to black labradorite with strong labradorescence is also mined in Madagascar and Norway, supplying a large volume of commercial material. The United States also features notable sources, such as the Oregon sunstone, a transparent variety of labradorite that contains copper inclusions creating a glittery effect known as aventurescence.
Labradorite formation requires a specific chemical composition, primarily a calcium-enriched plagioclase feldspar, with its anorthite percentage ranging between 50 and 70 percent. This composition allows for the formation of microscopic, parallel layers, or lamellae, of differing feldspar compositions within the crystal structure. The scattering and interference of light off these internal layers creates the characteristic labradorescence. These geological conditions limit the mineral’s occurrence to specialized magmatic environments, such as basalt, gabbro, and massive anorthosite complexes.
Identifying Labradorite in the Field
When seeking raw labradorite, the initial appearance can be deceiving, as specimens often present as a dull, translucent to opaque gray, white, or dark-gray stone. The mineral crystallizes in the triclinic system, which results in blocky or lath-shaped grains within the host rock. Collectors should look for these characteristic crystal shapes embedded in the surrounding matrix rock, such as anorthosite.
A definitive test for identification involves checking the stone’s physical properties, beginning with its hardness, which ranges from 6 to 6.5 on the Mohs scale. This hardness means the mineral is resistant to scratching by common objects, yet it is softer than quartz. Labradorite also exhibits two directions of perfect cleavage that intersect at an angle of approximately 86 degrees, meaning it tends to break along smooth, flat planes.
The most reliable method for field identification is testing for the labradorescence phenomenon itself. Since the color flash is often hidden beneath a weathered or dull surface layer, the stone must be rotated under direct light, such as sunlight or a strong flashlight. Tilting the specimen allows the light to hit the internal twinning planes at the correct angle to produce the iridescent flash. Wetting the surface can also temporarily enhance the visibility of the shimmer, helping to distinguish true labradorite from other common gray rocks.
Practical Collecting and Ethical Considerations
For individuals interested in field collecting, preparation and safety are important, especially when exploring remote or rocky geological sites. Appropriate safety gear, including safety glasses and durable gloves, should be worn to mitigate risk from rock fragments. A geologist’s hammer, a chisel, and a sturdy backpack are necessary tools for extracting samples from the surrounding matrix rock.
The act of rock hounding must be balanced with legal and environmental responsibilities. It is necessary to determine the ownership of the land before attempting any collection, as trespassing on private property without permission is illegal. Public lands, such as those managed by the Bureau of Land Management, often permit casual collection for personal use. However, national parks and state parks typically prohibit or severely restrict mineral collection, requiring collectors to check specific local regulations.
Practicing ethical collection means adhering to “Leave No Trace” principles to minimize environmental impact. Collectors should backfill any holes they dig to prevent hazards and erosion, and avoid disturbing vegetation or leaving behind litter.
For those who prefer a less strenuous approach to acquiring specimens, commercial sources offer a viable alternative. High-quality raw and cut labradorite is readily available at gem shows and through established mineral dealers.