Rock or Mineral?

When I go to sell rocks, one of question I hear is “Ok, but what exactly is the difference between a rock and a mineral?” That is an excellent question! Rocks and minerals are not actually synonyms – they’re closely related, but not the same thing. I like to think of it like the difference between a chocolate chip cookie, and a chocolate chip. A rock is a combination of minerals, just like a cookie is a combination of chocolate chips, flour, sugar and other ingredients (baking is not my strong suit). If you have a cookie with chocolate chips and walnuts, you can break up the cookie into different parts. In the same way, you can break a rock apart into the different minerals that it is made from, although depending on the type of rock, it might require something ranging from a rock hammer to an intense feat of chemistry.

To be precise, there are a few more criteria to distinguish rocks and minerals. A rock is a naturally occurring combination of minerals. Identification of a rock types is done by characterizing the minerals included in the rock, the texture or way the minerals are combined and the general origins of the rock (i.e. is it sedimentary, metamorphic or igneous). Similarly, there are a few more criteria for something to be a mineral: it must be naturally occurring, inorganic and have a specific crystalline building block that is stacked together in a regular, repeating way. Minerals can be identified by characteristics such as hardness, color, cleavage or preferential planes of breaking, streak color and optical properties.

Of course, this is only the tip of the iceberg. If you’re interested in geology, I highly recommend exploring your local natural history museum and joining a local geology club. If you want to delve into the world of mineralogy, there are a lot of great resources online for you. One of my favorites is a web series focused on understanding optical mineral properties. You can find it by searching for Will Snellius on YouTube.