JANUARY 2010 NEWSLETTER - Minerals and Mineral Classes Defined

Correctly identifying a rock from a crystal can be daunting.  Add in words like stone, mineral, gemstone, etc and many times what you have is confusion soup. When I first began working with crystals, EVERYTHING was a crystal (whether it geologically, scientifically, or accurately was or not).  I solved my lack of knowledge back then, by calling everything a "piece". "This piece is good for..."   This cloaked my lack of knowledge for a while.  My information on the "piece" was spot on, but my geological knowledge lacked tremendously.

Choosing to become more knowledgeable was not just a task I assigned myself at the time, it was imperative that I knew what I was talking about.  I was in the crystal business, I taught crystal classes.  I simply could not see myself teaching others if I did not understand the differences myself.   As I soon learned, it was not enough to understand the metaphysical aspects of these pieces, it was equally important to understand the geological aspects as well. And so, the quest began.

Let me share with you what I have learned about Minerals.

A mineral is (generally) an inorganic, naturally occurring, organized crystalline structure composed of a single chemical compound or element.  Let's break this down a bit more. 

There are four rules that define if a mineral:
1. Minerals must have a repetitive crystalline structure.
2. Minerals must have a determinable and precise formula.
3. Minerals must be natural.
4. Minerals must be inorganic.

So using this information, what do you think?
Is Amber a mineral?
Is Fluorite a mineral?
Is Moldavite a mineral?
How about Calcite?
Does Obsidian fit the criteria?

Let's break this down even further, step by step. I think you may be surprised :)

1. Minerals must have a repetitive crystalline structure.
What this tells us is that Minerals are classified as Crystals.  What is a crystal?
A crystal is a geometric solid that forms in a specific, repeating pattern.  Externally, the crystal is smooth and has an exacting symmetry which reflects the internal arrangement of its atoms.  When there is no specific repetitive structure, this is known as "Amorphous" and as such, cannot be identified as a mineral.  Obsidian, Jet, Amber, Fulgerites, Opal, and Tektites are all Amorphous meaning they cannot be classified as a Crystal and certainly not as a mineral.

2. Minerals must have a determinable and precise formula.
All minerals must have a precise formula.  This means that the chemical make up of the mineral must contain accurately measurable elements from the Periodic Table of Elements.  For instance, Silicon Dioxide(SiO2) is one part Silicon (Si) and two parts Oxygen (O2).  Some minerals, like Obsidian, cannot be accurately measured due to its creation process. Obsidian first comes into being with the occurrence of volcanic lava flows which pick up numerous impurities on its way down the mountain and is then cooled as it comes in contact with water.  Due to the massive amount of these impurities, they cannot be accurately measured or precisely plotted using the Periodic Table of Elements.  We know it is a type of volcanic silica glass, but all other impurities picked up along the way cannot be as easily identified if they can be identified at all.

3. Minerals must be natural.
All minerals must be natural.  This simply means that to be a true mineral, it must be a naturally occurring phenomenon.  They cannot be enhanced or manipulated in any way.

4. Minerals must be inorganic.
Minerals must, by their very definition, be inorganic.  Inorganic substances are of mineral origin, whereas organic substances are usually of animal or plant origin.  Case in point- Amber. Amber cannot be classified as a mineral due to the fact that it is fossilized plant resin.  Jet also falls into this category.  Both Jet and Amber are organic and amorphous in nature, which exclude them from being classified as a mineral.

A mineral must meet all four requirements. While many may pass one or two criteria, they are still not accurately categorized as a mineral.  A rock for example, occurs naturally (#3) and is inorganic (#4), however, it does not fall within the parameters of #1 and #2 (a crystalline structure, precise formula).  A rock is a consolidated material composed of grains of one or more minerals.

Minerals fall into one of eight classes.  You may see various sites include others, such as mineraloids and organics, but these are basically "extras" to fit pieces like Amber, Obsidian and Jet into since they do not meet all four specific criteria of a mineral.

Let us take a look at the Mineral Classes, one by one.  To keep this simple, the subclasses of each Class (and there are many) are being left out.  And while some of the information may be far too scientific (I know it was for me), it is fun to see where some of these minerals sit in relation to the classes themselves.

Silicate class
The largest group of minerals by far are the silicates (95% of all rocks are silicates), which are composed largely of silicon and oxygen, with the addition of ions such as aluminum, magnesium, iron, and calcium.  Some popular Silicates include ALL Quartz (Clear, Smoky, Amethyst, Citrine), the entire family of Beryl (Aquamarine, Emerald, Goshenite, Heliodor, Morganite, Bixbite), Danburite, Larimar, Peridot and Phenakite, just to name a few.

Carbonate class
The Carbonate minerals consist of those minerals containing the anion (CO3)2- and include calcite and aragonite (both calcium carbonate), dolomite (magnesium/calcium carbonate) and siderite (iron carbonate).  Carbonates are commonly deposited in marine settings when the shells of dead planktonic life settle and accumulate on the sea floor.  Carbonates are also found in evaporitic settings (e.g. the Great Salt Lake, Utah) and also in karst regions, where the dissolution and reprecipitation of carbonates leads to the formation of caves, stalactites and stalagmites.  The carbonate class also includes the nitrate and borate minerals.  Some well known Carbonates include Calcite, Aragonite, Malachite, Azurite, and Rhodochrosite.

Sulfate class
Sulfates all contain the sulfate anion, SO42-.  Sulfates commonly form in evaporitic settings where highly saline waters slowly evaporate, allowing the formation of both sulfates and halides at the water-sediment interface.  Sulfates also occur in hydrothermal vein systems as gangue minerals along with sulfide ore minerals.  Another occurrence is as secondary oxidation products of original sulfide minerals.  The Barite Group (Celesite, Angelsite and Barite), Anhydrite, and Gypsum belong in the Sulfate Class.

Halide class
The Halides are the group of minerals forming the natural salts and include Fluorite (calcium fluoride), Halite (sodium chloride), Sylvite (potassium chloride), and sal ammoniac (ammonium chloride).  Halides, like sulfates, are commonly found in evaporitic settings such as playa lakes and landlocked seas such as the Dead Sea and Great Salt Lake. 

Oxide & Hydroxide classes
Oxides are extremely important in mining as they form many of the ores from which valuable metals can be extracted.  They also carry the best record of changes in the Earth's magnetic field. They commonly occur as precipitates close to the Earth's surface, oxidation products of other minerals in the near surface weathering zone, and as accessory minerals in igneous rocks of the crust and mantle. The oxide class includes both oxide and the hydroxide minerals. The Corundum group (Ruby, Sapphire), as well as Hematite, Magnetite and Spinel are all members of the Oxide and Hydroxide Class.

Sulfide class
Many sulfide minerals are economically important as metal ores.  The Sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, and the sulfosalts (sulfur and a second anion such as arsenic).  Members of this class include Galena, Pyrite and Cinnabar.

Phosphate class
The Phosphate mineral group actually includes any mineral with a tetrahedral unit AO4 where compound A can be phosphorus, antimony, arsenic or vanadium.  By far the most common phosphate is Apatite which is an important biological mineral found in teeth and bones of many animals.  Members of the Apatite Group (Apatite, Mimetite, Pyromorphite, and Vanadinite), Brazilianite and Turquoise are members of the Phosphate class.

Element class
The elemental group includes metals and intermetallic elements (Gold, Silver, Copper), semi-metals and non-metals.  While you may think that a Diamond is a member of the Silicates class, it is actually a member of the Element class, being made up from Carbon.

So let's recap using the KISS (Keep it simple spiritually) method-

• A rock is not a mineral since it only meets two out of four criteria.
• A rock is not a crystal (even though on occasion we call Diamonds, rocks...as in, "Wow! Look at that rock!"
• A crystal is a mineral. It meets all four criteria.
• Amorphous is defined as "not having a repetitive crystalline structure" and there for cannot be minerals. Amber is a good example of this.
• There are 8 accepted Mineral Classes and numerous sub classes which further help to categorize and identify minerals.

Thank you for walking with me through the forest of Geology.  I hope you have enjoyed reading the information as much as I have enjoyed presenting it to you.

with love and crystal blessings,
Kristi Huggins
Author and Project Manager for Healing Crystals

References:
http://www.crystalwiki.com/tiki-index.php
http://www.mindat.org/
http://en.wikipedia.org/wiki/Main_Page
http://www.galleries.com/

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