Molcajete

A molcajete (mo̞lkaˈxe̞te̞ or mol-cah-hay’-tay; Mexican Spanish, from Nahuatl molcaxitl) is a stone tool, the traditional Mexican version of the mortar and pestle, similar to the South American batan, used for grinding various food product.

The molcajete was used by pre-Hispanic Mesoamerican cultures, including the Aztec and Maya, stretching back several thousand years. Traditionally carved out of a single block of vesicular basalt, molcajetes are typically round in shape and supported by three short legs. They are frequently decorated with the carved head of an animal on the outside edge of the bowl, giving the molcajete the appearance of a short, stout, three-legged animal. The pig is the most common animal head used for decoration of this type. The matching hand-held grinding tool, known as a tejolote (Mexican Spanish, from Nahuatl texolotl), is also made of the same basalt material.

Molcajetes are used to crush and grind spices, and to prepare salsas and guacamole. The rough surface of the basalt stone creates a superb grinding surface that maintains itself over time as tiny bubbles in the basalt are ground down, replenishing the textured surface.

A new basalt molcajete needs to be "broken in" because small grains of basalt can be loosened from the surface when it is first used and this will give an unpleasant gritty texture to the first few items prepared in it. A simple way to do the initial "seasoning" is to grind uncooked white rice in the molcajete, a handful at a time. When the white rice flour has no visible grains of basalt in it, the molcajete is ready to use. Some rice flour may remain ground into the surface of the molcajete, but this causes no problems.

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Wikipedia