1. The volcanic activity in the area caused the rocks to silicify over time.
这个地区的火山活动导致岩石随着时间的推移逐渐硅化。

2. Fossils can undergo a process of silicification, where minerals replace the organic materials and turn them into silica.
化石可以经历硅化的过程，其中矿物质取代有机物质并将其变成二氧化硅。