Specimen grade hyalite comes from many places that have opal deposits but ONLY in the state of Utah, USA is gem quality adularescent material found in veins/seams thick enough to cut gemstone cabochons! The small deposits in Utah are depleted of the cabbing quality! Satin flash opal is indeed very rare and VERY hard to find!
Hyalite opal was formed by hot spring geyser deposits and does not have colorplay like other opal, instead the light rolls off the internal bubble structure and flashes back at the onlooker.
This cab of satin flash opal is a very nice stone. It could have a bit more of the flash. The adularescent flash is good, just not in the entire stone and is directional. but it is very clear like petrified ice and has no cracks.