Labradorite is a feldspar mineral that is most often found in mafic igneous rocks like anorthosite, basalt, gabbro, and norite. Some specimens of labradorite exhibit a Schiller effect, which is a strong play of iridescent blue, green, red, orange, and yellow colors as shown in the photographs. The phenomenon in which Labradorite is so well known for (the spectacular displays of color) is known as "labradorescence." Specimens with the highest quality labradorescence are often selected for use as gemstones.
Labradorescence is not a display of colors reflected from the surface of a specimen. Rather, light enters the stone and strikes a twinning surface within the stone, then reflects from it. The color seen by the observer is the color of light reflected from that twinning surface. Different 'twinning' surfaces within the stone reflect different colors of light, and light reflecting from different twinning surfaces in various parts of the stone can give the stone a multi-colored appearance.
Labradorite was thought of by the Ancient Inuits as the "Frozen Fire of the Aurora Borealis." Legends tell stories of an Inuit warrior who found a cave with the Aurora Borealis embedded within the rocks, on the shoreline of Labrador, Canada. The warrior attempted to release the Aurora Borealis with his spear but was unable to remove it all, leaving some of the light imprisoned in the rocks forever. The native inhabitants used the gemstone for medicinal purposes, and believed that it would increase their energy, while simultaneously relieving stress and anxiety.
References:
Geology.com - Labradorite