Can you name some minerals off the top of your head? You likely came up with things like gold, silver, copper and coal. These are all correct, but there are many more minerals on Earth - over 4,000 in fact! To understand what makes a mineral a mineral, we need to understand the basic requirements that categorize them, as well as their properties. (Read The Complete Classification of Minerals)
In order for something to be a mineral, it must first meet four criteria:
First, all minerals are solid. So, while water may contain minerals, water itself can't be a mineral because it's liquid.
Minerals are all naturally formed. This means they can't be manufactured in a lab. Synthetic gems, like cubic zirconia, are therefore not minerals.
All minerals have a unique and specific chemical composition. This is like the DNA of the mineral - it's what makes the mineral different from other minerals.
Lastly, all minerals have a crystalline structure. Minerals are some of the most beautiful substances on Earth, because they are always arranged in an orderly geometric pattern. Minerals of the same type always have the same geometric arrangement of their atoms.
Minerals are classified by their chemical composition and crystal structure. These two features occur on a microscopic level, but we can see them in other ways because they determine a mineral's observable physical properties. In other words, what appears to us on the outside is determined by what's on the inside.
Crystal form is the outward expression of the orderly arrangement of atoms inside the mineral. What you are seeing is the actual arrangement and structure of the atoms in that mineral. For example, look at some everyday table salt, which is a combination of sodium and chlorine. Normally, what you see is a salt cube, but if you were to break this cube down into smaller parts, it would simply break into smaller and smaller cubes because that is how the atoms are arranged.
Hardness is how resistant a mineral is to scratching, not how easily it breaks. Hardness depends on the bonds within the mineral, so the stronger the bonds, the harder the mineral. Mineral hardness is measured on theMohs scale of hardness, which compares the hardness of different minerals.
Diamond is considered the hardest mineral, so it's a 10 on the Mohs scale of hardness. Talc has a very weak bond between its atoms, and so it's a 1 on the Mohs scale of hardness. If it helps, you can think of the hardness of talc in relation to the hardness of your fingernail, which is about a 2.5.
Fracture and cleavage describe how a mineral breaks. Some minerals break very nicely along smooth planes, and this is called cleavage. Minerals that break this way do so because their atoms are arranged so that they break apart from each other along these planes. Mica is an example of a mineral that has cleavage. If a mineral fractures, it breaks in uneven ways that are not flat or parallel. Again, these minerals break like this because that's how their atoms are arranged.
Luster is how reflective a mineral is. Minerals are usually either classified as having metallic luster, which is very shiny or reflective, or non-metallic luster, which is not shiny and is very dull.