Opal
O'PAL, noun [Latin opalus or opalum.] A stone of the silicious genus, and of several varieties. It is one of the most beautiful of this genus, by reason of its changeableness of color by reflection and refraction. Kirwan distributes opals into four families, opal semi-opal, pitch stone [pechstein, ] and ligniform. Jameson divides opal into seven kinds.
Opal is a subspecies of indivisible quartz.