Hello! Here we go again, exploring the crystals world! We already made a little introduction about crystals and seen how to cleanse them. Today we’re going a little bit more in-depth, we’ll classify crystals under a scientific point of view: minerals, rocks, crystals and gemstones.
I mentioned that on our Planet there are tons and tons of different varieties of crystals and we have seen how to categorize them based on shape, colour and type. There is another classification we should make, a more technical and scientific one. It is common to read and use the general term “crystals“, even though it’s not precise. The categories I’m talking about are minerals, rocks and of course, crystals. Then we have a sub-category, gemstones. The main point that makes the difference between them is composition.
Minerals: they’re made by one, and only one chemical composition. When it’s more than one, then it’s more appropriate to define them as rocks. The IMA (International Mineralogical Association) has drawn up four main characteristics needed to consider a mineral:
- “It must be a naturally occurring substance formed by natural geological processes”. This means that all the “crystals” that have been made up artificially by human hands, or are a product of a living being (such as crystals parts in plant tissues) and seashells, can’t be defined as minerals.
- It must be a solid substance in its natural occurrence. This point doesn’t need any further explanations, even though I must mention a couple of exceptions. Water in its “basic” state – liquid- isn’t, of course, considered a mineral, but ice is a mineral. Native mercury is classified as a mineral in its solid-state.
- It must have a well-defined crystallographic structure. On a macroscopic level, the characteristics are hardness, cleavage and form.
- It must have a fairly well-defined chemical composition.
In 2020, IMA has officially approved around 5,000 different minerals. Some examples are sapphirine, siderite, roselite, rubicline, ameghinite. If you wish to have a look at the complete list approved by IMA, here’s their official website
Rocks. Geologist, as mentioned before, define rocks as “A bound aggregate of minerals, mineraloids, or fragments of other rocks.”. Rocks can be classified into three major categories:
- Igneous: formed from the crystallization of magma
- Sedimentary, compacted deposits of other particles of rocks
- Metamorphic, the result obtained when a rock changes its original mineralogy because of conditions such as temperature or pressure.
Some examples of rocks are basalt (1), limestone, sandstone (2), quartzite and marble (3). If you wish to consult a full list, here’s one
Crystals. This last major category includes nothing but minerals which microscopic components are arranged following a particular scheme (or structure). On a macroscopic level, instead, they usually show a specific geometrical shape. Considering this, even snowflakes are, technically, crystals. Examples of crystals are fluorite, quartz, desert rose. Here’s a list of crystals. I also mentioned a sort of sub-category, the gemstones, which are parts of mineral crystals that have been polished and treated, usually used for jewelry purpose. We do have few exceptions into this category, such as lapis-lazuli (rocks) and amber, that are gemstones despite the fact they’re not scientifically minerals.
We can divide gemstones into precious (diamond, ruby, emerald, sapphire) and semi-precious (all others). The term precious has been coined around ‘800 to refer to the four mentioned minerals and divide them from the rest. Their quality is valued on the richness of their colours (opposite for diamond) and their translucence. Needless to say that the gems included in this category are usually more expensive. I say “usually” because there are some semi-precious gems that are more expensive than a mid-quality sapphire, for instance. So don’t let words trick you, contextually there is a difference between semi-precious and precious, but it is strictly from a commercial perspective.
I hope this second part of the introduction about crystals was interesting and useful for you…Even though it was under a more scientific point of view!
I’ll see you soon, stay tuned!