The term mainly refers to stones such as rubies, sapphires, emeralds and so on. Things like aquamarine, zircon, opal, turquoise, cat's-eye, agate, amber, coral, and amethyst etc. What you would call precious and semi-precious stones in English then. The jewelry business is heavily affected by prevailing business conditions, I understand, and the Japanese jewelry market, which had previously enjoyed rapid growth, is now in the doldrums due to the collapse of the bubble economy.
Imports vary considerably from year to year.
They grew steadily from 1985 as a result of the impact of the abolition of the commodity tax, the jewelry boom, and the strong yen, and peaked in value terms in 1990. Prices have subsequently dropped due to the slump in domestic consumption. Now what are being imported are not high quality but rather cheap gems. Since 1995, there has been a conspicuous fall in demand for semi-precious stones, and imports of colored stones in 1998 were less than half what they were five years earlier in terms of volume. The reason for this is that the use for costume jewelry has dropped precipitously.