Labradorite.

Labradorite is a calcium-rich plagioclase feldspar with a remarkable optical property called labradorescence. The flash of blue, gold, green, or occasionally violet that seems to drift across the surface is not pigment but interference, light scattering off thin internal lamellae of slightly different feldspar composition. Tilt the stone past the right angle and the colour vanishes back into ordinary grey rock.

The mineral was first described from the Labrador peninsula in Canada in the 1770s, which gave it the name. Madagascan labradorite supplies most of the strong-flash material in the modern trade, with Finnish spectrolite reserved for the rare pieces that show the full spectrum. The grey of an unflashing piece can be misleading until you turn it under a window.

In modern crystal practice labradorite sits with the third eye and throat chakras, and is the stone people most often choose for transition: leaving a job, ending a relationship, the strange in-between weeks of grief or restructuring. Its quiet quality matches the moment. It rarely announces itself but rewards attention. A piece on a desk or in the pocket is happy, and the hardness is good enough for a polished cabochon to wear well in a pendant. Avoid steam and ultrasonic cleaners, which can stress the internal lamellae.