A lozenge has a diamond shape A lozenge cut stone is a step-cut gem with a diamond shape LUSTER A stone's luster is its sparkle or sheen - the way it relects light The luster depends on the nature of the stone's surface reflectivity Some types of luster include: adamantine (also called brilliant or diamondlike, like a faceted diamond), earthy (with little reflectivity- also called dull, like shale or clay), greasy (like nepheline or apatite), metallic (also known as splendent, like pyrite or marcasite), resinous (like amber), pearly (with an iridescent reflectivity, like pearls or mica), pitchy (tarry minerals that are radioactive, like uraninite), silky (with a fibrous structure, like some tiger's eye or satin spar), vitreous (also known as glassy, like olivine, transparent quartz, or obsidian), and waxy (like halite or turquoise) A pearl's luster is derived from its nacre