Labradorite

At first glance labradorite looks like a dark grey, fairly modest stone. Then you turn it, and it lights up in blue, green, gold and sometimes orange. That is exactly what happens in the stones in the photo: part of the surface flashes blue, and part gold.

This effect is called labradorescence. Labradorite is a feldspar of the plagioclase group, a relative of moonstone. When the rock it forms in cools very slowly, very thin layers of slightly different composition develop inside the crystal. According to Wikipedia, when the spacing between these layers is about 128 to 252 nanometers, the light reflected from them creates color. The color changes with the angle, and at some angles it disappears completely. So if your stone suddenly looks grey, it is not broken. Just turn it.

The name comes from the Labrador Peninsula in Canada. According to Geology.com, a Moravian missionary discovered it in 1770 on Paul's Island, near the village of Nain. According to Wikipedia, it is also found in Finland, Norway, Madagascar, China, Australia and the United States.

Finland has labradorite with an especially rich range of colors, called spectrolite. According to Wikipedia, the deposit was discovered in 1940, while a line of fortifications was being built there during World War II. Fortifications are not usually built to find gemstones, but this time it happened.

You may have seen labradorite without knowing it: according to Hebrew Wikipedia, near the city of Zhytomyr in Ukraine, a rock made mostly of labradorite is quarried and sawn into slabs for kitchen countertops. Not every kitchen counter can say it is related to a gemstone.