Here are some possibilities:
Rocks with hard, non-porous crystals in distinct layers:
* Foliated metamorphic rocks: These rocks are formed under intense pressure and heat, which causes their minerals to align in parallel layers. Examples include:
* Schist: Often contains distinct layers of mica, which gives it a shiny, layered appearance.
* Gneiss: Has alternating layers of light and dark minerals, creating a banded look.
* Slate: Has very fine-grained layers, often used for roofing.
Rocks with hard, non-porous crystals forming a dense structure:
* Quartzite: A metamorphic rock formed from sandstone, with tightly interlocked quartz crystals. It's very hard and resistant to weathering.
* Marble: A metamorphic rock formed from limestone, with recrystallized calcite crystals. While it can have a layered appearance, the layers are less pronounced than in foliated rocks.
* Igneous rocks: Some igneous rocks, like granite, can have hard, non-porous crystals formed from the slow cooling of magma. However, they don't typically exhibit layering in the same way as metamorphic rocks.
Important considerations:
* Porosity: While these rocks have hard crystals, they may still have some porosity depending on the size and arrangement of the crystals.
* Definition of "layer": The term "layer" can be ambiguous. If you're referring to distinct bands of different minerals, then foliated metamorphic rocks are the best fit. If you're referring to a more general layering within the rock structure, other options like quartzite or igneous rocks might be more appropriate.
To give you a more specific answer, it would be helpful to have more information about the rock you're looking for.
