题目选项分析

The varieties of semi-precious gemstones considered chalcedony are composed of silica and feature fine intergrowths of quartz and moganite, which themselves consist of silica and are distinguished only by their crystal structures.

The varieties of semi-precious gemstones considered chalcedony are composed of silica and feature fine intergrowths of quartz and moganite, which themselves consist of silica and are distinguished only by their crystal structures.