* Obsidian is an igneous rock: Obsidian forms from rapidly cooled volcanic lava. It's glassy, hard, and brittle.

* Shale is a sedimentary rock: Shale forms from layers of fine-grained sediment, like clay, silt, and organic matter, that accumulate and are compressed over time.

The Relationship:

* Weathering and Erosion: Obsidian, exposed to the elements, will eventually break down into smaller pieces through weathering (chemical and physical processes).

* Transportation: These smaller pieces, along with other sediments, can be carried by wind, water, or glaciers and deposited elsewhere.

* Compaction and Cementation: Over long periods, these layers of sediments become compacted and cemented together, eventually forming shale.

In summary: Obsidian's transformation into shale involves a complex process of weathering, erosion, transportation, and sediment accumulation, but it doesn't directly change into shale.