General terms:
* Powder color: This is a simple and descriptive term.
* Streak color: This term is used in geology to describe the color of a mineral's powder when rubbed against a streak plate (unglazed porcelain).
* Mineral color: This term is often used in the context of identifying minerals, as the powder color can be a useful diagnostic feature.
More specific terms:
* Clay color: This is used to describe the color of clay, which is a type of rock powder.
* Ocher color: This refers to the yellowish-brown color of a specific type of clay powder.
* Vermilion color: This refers to the bright red color of a specific type of pigment made from mercury sulfide, which is a mineral powder.
The most appropriate term will depend on the specific rock and the purpose of describing its powder color.
