Here are some examples of such rocks:

* Granite: This igneous rock is very dense with tightly packed crystals, making it difficult for fluids to pass through.

* Basalt: Another igneous rock with a similar structure to granite, making it impermeable.

* Quartzite: This metamorphic rock is formed from sandstone, and the high pressure and heat during its formation create a dense, non-porous rock.

* Marble: This metamorphic rock, formed from limestone, can also be impermeable depending on the degree of recrystallization.

* Shale: This sedimentary rock is made of very fine clay particles tightly packed together, making it difficult for fluids to pass through.

Porosity refers to the amount of empty space in a rock. Permeability refers to the ability of fluids to flow through the interconnected pore spaces.

Rocks with low porosity and permeability are important in a variety of contexts:

* Aquifer sealing: They can act as barriers to groundwater flow, preventing contamination from migrating.

* Oil and gas exploration: They can act as seals, trapping oil and gas reserves.

* Construction: Their durability and impermeability make them ideal for building materials.

Let me know if you would like to know more about any of these rocks!