Plasma , a deep green agate quartz, with irregular, whitish-yellow spots. This variety, though known to and worked by the ancients, has never been found except in the clearings of the ruins at Rome. Some specimens, however, have been referred to Mount Olympus.

Lapis-Lazuli, when calcined, is soluble to the consistency of a jelly in acids, and under the action of continued heat fuses to a white enamel; scratches glass; fracture smooth, with a close grain.

Large deposits, but of an inferior quality, occur in Siberia, and thick strata are found also in Chili. The finer sorts come from Persia, Anatolia, and China. But in the latter country, it is imitated with a perfection dangerous for the amateur collector.