A variety of Opal with formula SiO2•n(H2O) and hardness 5.5-6.5.
Opal-AN is a term for amorphous opal with a glass-like structure (Graetsch, 1994). The "A" in the name stands for amorphous; the subscript "N" is to imply its structure is network-like similar to silica glass; however, it still contains about 3-8% water, both as molecular water and bound in silanole (SiOH) groups.
Because it has a different structure, it does not show the opalescence (play of color) that is found in precious opal.
Hyalite occurs as globular and botryoidal masses and irregular crusts in volcanic and pegmatite environments where the silica deposits from the gas phase (Flörke et al, 1973). It often shows a strong green fluorescence in UV light. ( from Mindat)
This material is very attractive when seen under short wave,it glows like a lamp!
It comes from Tarcal,Zemplen,Hungary.This gem has been cut by Luigi Mariani and it has some small flaws on one side.