水晶 (shuǐjīng) means "crystal," referring to a clear, transparent mineral or gemstone. It is used both for natural quartz crystal and as a material descriptor, as in 水晶球 (crystal ball).
她戴着一条漂亮的水晶项链。
Tā dàizhe yī tiáo piàoliang de shuǐjīng xiàngliàn.
She is wearing a beautiful crystal necklace.
桌上摆着一个透明的水晶球。
Zhuō shàng bǎizhe yī gè tòumíng de shuǐjīng qiú.
There is a transparent crystal ball on the table.
这家店卖的水晶饰品都是手工制作的。
Zhè jiā diàn mài de shuǐjīng shìpǐn dōu shì shǒugōng zhìzuò de.
The crystal accessories sold at this shop are all handmade.