The moldavites belong to tektites. It means they were formed in (or better to say “just before”) a meteorite impact. If a meteorite hits the ground at a place with porous rock rich in silica, the material is melted and turned into a glassy substance.
Occasionally, the liquid melt can be ejected (in fact splashed in flying masses) hundreds or even thousands of kilometers away from the crater. Bits of the molten material then solidify while still airborne,or immediately after they fall on the ground. This happened in Europe approx. 15 million years ago.
Tektites generally and moldavites particularly are typical of pits, chutes, furrows and other features sculptured on their surfaces. Such sculpturing can be attributed to slow and uneven dissolution of the stone’s surface by ground water seeping slowly through the rock wherein the stone is deposited.
99 % of all moldavite finds have provided the South Bohemian localities, 1% were found in South Moravian localities, tens of pieces were found in the Lusatian area (near Dresden, recently even few pieces in Poland), Cheb basin area (West Bohemia) and Northern Austria (Waldviertel, near Radessen)