Let’s put this geology degree I have to good use why don’t we?
I know that a lot of people who come upon this page may want to know more of the scientific background behind a lot of the crystals I talk about, and I will do as much as I can to address the most important things in those individual posts. I always welcome questions as well!
So for those who know nothing about rocks or some, (we all have to start somewhere) here is a geology 101 refresher!
Let’s start with minerals (or more so commonly what we might think of crystals).
Minerals are the building blocks for rocks. Minerals are the smallest individual grains or atoms/molecules in a rock if you want to go to the smallest scale. There are five criterion that a substance must make in order for it to be officially called a mineral.
- 1. It must be solid
- 2. It must be crystalline
- 3. It must be inorganic
- 4. It must have a definite chemical composition
- 5. It must naturally occurring
So let’s break these down. First lets start with the easy ones, it must be solid and must naturally occurring. Now let’s get into the nitty gritty. A crystalline structure refers to the structure that the individual molecules form all the way up to the actual formation of the crystal that you can hold in your hand. A common crystalline structure is cubic, just like a halite (salt) would form.
Next we have that it must be inorganic. This means that it must not have been produced by biological processes or living organisms such as a limestone where you can sometimes see small sea shells and corals inside the rock. Next we have that it must have a definite chemical composition. Referring to the above image, we see that halite is formed from one sodium anion and one chlorine ion. Every single halite will have this chemical formula as its base structure. And lastly it must be naturally occurring, aka it cannot be man made. (However, this does not apply for lab created gemstones- you be the judge on whether or not those are “real” minerals- they are just as pretty!).
So that takes care of minerals. Next we will move onto rocks!
Rocks are conglomerates of different minerals. There are three basic categories for rocks- sedimentary, metamorphic, and igneous.
Sedimentary rocks are formed from the layering of sediments over a long period of time. The laws of uniformitarianism tell us that the deeper you go into the earth, the older a rock is and vice versa (naturally assuming that the newest portion of a rock is at the surface). Rocks that are in this category are lithified (creation of rocks) by intense pressures and heat from the earth’s mantle. Minerals such as quartz and feldspars are most common in sedimentary rocks. They are the most common rocks found in West Virginia (where I currently live). Examples of sedimentary rocks include sandstones, limestones, slate, shale, and mudstones. The grain sizes and colors that we see in sedimentary rocks are indications of where and how they were formed. For example sandstones and limestones are usually created in either beach or desert environments, while mudstones are created in swampy muddy environments. Rock salt forms from evaporation of water, another category of sedimentary rocks called evaporites.
Next we have igneous rocks.
Igneous rocks are formed in high temperature environments, in or near volcanic structures. There are two types of igneous rocks, intrusive and extrusive. Intrusive are formed inside the Magma chamber of a volcano, and extrusive the opposite being ejected into the air during an eruption. Whichever way the rock was formed indicates the grain size of the rock, with extrusive rocks cooling rapidly not allowing for distinct crystal formations to occur. Intrusive rocks cool and condense over long periods of time, giving them the opportunity to create large visible crystals within the rocks. The more silica content an igneous rock has (quartz and feldspars) it is lighter colored and considered to be felsic. If it is dark and showing little quartz and feldspar content it is considered to be mafic.
Lastly, we have metamorphic rocks. These rocks are essentially a combination of sedimentary and igneous rocks. A rock always will start out as either igneous or sedimentary. It is once either rock is exposed to extreme heat and pressure that it becomes metamorphic. The degree of temperature and amount of pressure is what determines what metamorphosed rock it is. The parent rock (either igneous or sedimentary rock to start out with) is called the protolith, and protoliths can be metamorphosed many times. 
Lastly, all of these great rocks come together to form the rock cycle!
If you have any questions about rocks, minerals, or their formations feel free to contact!
365 Days of Spirit 