Salt is a mineral, but the plastic making up an inexpensive pen is not. Why not?

In order to differentiate between a mineral (salt) and non-mineral (plastic), we first need to understand the characteristics and definition of a mineral. A mineral is a naturally occurring inorganic substance that has a specific chemical composition and a definite crystalline structure.

Minerals have some characteristics that can help us distinguish them. These characteristics include: 1. Naturally occurring - Minerals are formed through natural geological processes. 2. Inorganic - Minerals are not made of organic compounds, meaning they do not come from living organisms. 3. Chemical composition - Each mineral has a specific chemical composition, which means it is made of certain chemical elements or compounds. 4. Crystalline structure - Minerals have a definite structure in which their atoms or ions are arranged in an organized and repeating pattern.

Now, let's take a look at the characteristics of plastic to understand why it is not a mineral. 1. Man-made - Plastics are synthetic materials, which means that they are made by humans through chemical processes, not naturally occurring geological processes. 2. Organic - Plastics are made from organic materials, most commonly being derived from petroleum products. This means that the source of plastics is from living organisms (plants and animals). 3. Variable composition - Plastics can have different compositions, depending on the type and purpose of the plastic. 4. Non-crystalline structure - Most plastics do not have a definite crystalline structure as minerals do; instead, they often have an amorphous or disordered molecular arrangement.

Based on the characteristics of minerals and plastic, we can conclude that plastic found in inexpensive pens is not a mineral because it is man-made, organic, has a variable composition, and does not have a definite crystalline structure. In contrast, salt is a mineral because it meets all the criteria: it is naturally occurring, inorganic, has a specific chemical composition, and a definite crystalline structure.