GEM STONES

Listing description The mineral or gemstone chrysoberyl , not to be confused with beryl , is an aluminate of beryllium with the formula BeAl 2 O 4 . [1] Despite the similarity of their names, chrysoberyl and beryl are two completely different gemstones . Chrysoberyl is the third-hardest frequently encountered natural gemstone and lies at 8.5 on the hardness scale , between corundum (9) and topaz (8). [2] Detailed description An interesting feature of its crystals are the cyclic twins called trillings . These twinned crystals have a hexagonal appearance, but are the result of a triplet of twins with each "twin" oriented at 120 o to its neighbors and taking up 120 o of the cyclic trilling. If only two of the three possible twin orientations are present, a "V"-shaped twin results. Ordinary chrysoberyl is yellowish-green and transparent to translucent . When the mineral exhibits good pale green to yellow color and is transparent, then it is used as ...

Listing decription Chrysoprase , chrysophrase or chysoprasus is a gemstone variety of chalcedony (a cryptocrystalline form of silica ) that contains small quantities of nickel . Its color is normally apple-green, but varies to deep green. The darker varieties of chrysoprase are also referred to as prase . (However, the term prase is also used to describe chlorite -included quartz, and to a certain extent is a color-descriptor, rather than a rigorously defined mineral variety.) Detailed description Chrysoprase , chrysophrase or chysoprasus is a gemstone variety of chalcedony (a cryptocrystalline form of silica ) that contains small quantities of nickel . Its color is normally apple-green, but varies to deep green. The darker varieties of chrysoprase are also referred to as prase . (However, the term prase is also used to describe chlorite -included quartz, and to a certain extent is a color-descriptor, rather than a rigorously defined mineral variety.) Chrysoprase is c...