The worn igneous rock that wears into grains of sand and clay is called igneous bedrock.

Here's a breakdown:

* Igneous rock: Formed from the cooling and solidification of molten rock (magma or lava).

* Bedrock: The solid rock layer beneath the soil and other loose materials.

* Weathering: The process of breaking down rocks, soil, and minerals through contact with the Earth's atmosphere, water, and biological organisms.

Weathering processes like wind, water, and ice break down igneous bedrock over time. This breakdown creates smaller and smaller pieces, eventually resulting in:

* Sand: Made up of mineral grains that are typically between 0.0625 and 2 millimeters in diameter.

* Clay: Made up of very fine-grained particles that are less than 0.0039 millimeters in diameter.

So, while it's not a specific type of igneous rock, it's the process of weathering that breaks down any type of igneous bedrock into sand and clay grains.