Lake Salda in SW Turkey seems to be a very spectacular place, especially geologically. It is a crater lake with sandy shores but this sand is not made of quartz or some other usual mineral. It is bright white and composed of hydromagnesite.
Hydromagnesite is a Mg-bearing hydrated carbonate mineral. It is usually an alteration product of brucite which is a magnesium hydroxide and occurs in dolomitic marble and serpentinite. In this case there is little doubt that this sand comes from serpentinite rocks because there are lots of serpentinite fragments among the sand grains. Serpentinite is a rock type that is composed of serpentine minerals which were formerly ultramafic igneous rocks. All these alterations are hydrothermal. It means that hot water circulating in the rocks carried out these reactions.
Sand from the southern shore of Lake Salda in Turkey containing hydromagnesite (white) and serpentinite (dark grains). The bright color of the sand is easily visible even in satellite maps. The width of the view is 15 mm.