ROCK CRYSTAL IS A FORM OF TRANSPARENT QUARTZ. IN PLINY'S DAYS, ROCK CRYSTAL WAS "THE MOST COSTLY PRODUCT ON THE EARTH'S SURFACE", MUCH MORE VALUABLE THAN GOLD OR SILVER. IN ANCIENT TIMES IT WAS MINED IN ASIA, CYPRUS, ALPINE MOUNTAINS; BUT ROCK CRYSTAL THAT ORIGINATED FROM INDIA WAS MOST IN DEMAND.
CARNELIAN IS A SPECIES OF CHALCEDONY, REDDISH IN COLOR BECAUSE OF IT'S IRON INCLUSIONS.
PLINY SAID THAT "NO OTHER STONE WAS MORE IN USE THAN CARNELIAN".
AMETHYST IS A variety of quartz, differing from common quartz and rock crystal chiefly because of its violet to purple color, which is caused by the presence of compounds of iron or manganese. PLINY SAID THAT THE HIGHEST QUALITY AMETHYST Came FROM INDIA, HOWEVER IT WAS ALSO MINED IN ASIA MINOR, ARMENIA, EGYPT, SYRIA AND CYPRUS. AMETHYST WAS NOT COMMONLY USED IN THE ANCIENT WORLD.
Agate IS a CRYPTO-CRYSTALLINE FORM of quartz WITH DIFFERENT-COLORED WAVY BANDS. ACCORDING TO PLINY THE AGATE WAS MORE POPULAR IN TIMES PREDATING HIS OWN.