Belomorite (Russian: беломорит), sometimes peristerite, moonstone, murchisonite, Ceylon opal, or hecatolite, is a decorative variety of albite (oligoclase) of white or light gray color with a distinct iridescence effect. By composition, belomorite belongs to the feldspar family; it is a sodium aluminosilicate from the plagioclase group, in most cases belonging to the isomorphic series albite (Ab) — anorthite (An) with an approximate percentage of 70Ab-30An.

The name “belomorite” was given to this variety of albite by academician Alexander Fersman in 1925, based on the location of its discovery near the shore of the White Sea (Russian: Белое море, romanized: Beloye more), and also, by association, for the similarity of iridescence colors with the shades of sea water. The best varieties of belomorite are translucent or transparent, they have a pearl-glass luster and iridescence in blue, gray-blue, violet-blue, greenish-blue or pale violet tones. The most famous deposits of this gem are in the north, in the pegmatites of the Kola Peninsula and Karelia.

Belomorite is a spectacular and popular jewelry and ornamental material, one of the varieties of moonstone. However, due to its fragility and perfect cleavage, the mineral often breaks and is difficult to process, so it is cut in the form of simple cabochons (oval, round, teardrop-shaped), as well as balls or polished plates.

A decade and a half after the discovery of this variety of albite near the White Sea coast, Alexander Fersman described the history of his “find” in sufficient detail and accurately in a short lyrical essay entitled “Belomorite.” Together with his companion, he got off the train at the Arctic Circle station [ru] in the Loukhsky District of the Republic of Karelia and they set off together towards the “Blue Pale” — that was the name of the mined-out vein of feldspars, located in the middle of a swampy area, between hills (in Karelian - varaks) almost on the very shore of the White Sea, about six kilometers east of the station.

There, in an old working, among dark amphibole shales, there was a snow-white vein of albite at least ten meters long, it rose to the top of the neighboring hill and went with lateral branches into the dark stone of shale rocks. Alexander Fersman sat down near a stack of feldspar, folded for transportation, looked at it carefully and, as he writes, could no longer look away, — in front of him was “a white, barely bluish stone, barely translucent, barely transparent, but clean and even, like a well-ironed tablecloth.”

The stone was split along individual shiny surfaces, and some mysterious light played on these edges. These were gentle bluish-green, barely noticeable iridescences, only occasionally they flashed with a reddish light, but usually a continuous mysterious moonlight flooded the entire stone, and this light came from somewhere from the depths of the stone — well, just like the Black Sea burns with blue light in autumn evenings near Sevastopol.

The delicate pattern of the stone from some thin stripes crossed it in several directions, as if imposing a mysterious lattice on the rays emanating from the depths. I collected, selected, admired and again turned the moonstone towards the sun.

The stone found in an old mine was called “belomorite” — because, as Fersman explains, “The White Sea shimmered with the colors of moonstone... or did the stone reflect the pale blue depths of the White Sea?..” — Geologists took several samples to the Peterhof lapidary factory [ru], recommending it as a new jewelry stone.