Fossils are usually formed in the _______rocks.

Explanation

**Step-by-Step Solution:**

1. **Understanding Fossils**: Fossils are the preserved remains or traces of ancient organisms that lived millions of years ago. They provide valuable information about the history of life on Earth.

2. **Types of Rocks**: There are three main types of rocks: igneous, metamorphic, and sedimentary. Each type of rock forms under different conditions.

3. **Formation of Sedimentary Rocks**: Sedimentary rocks are formed from the accumulation and compaction of mineral and organic particles. This process occurs at relatively low temperatures and pressures compared to igneous and metamorphic rocks.

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