Different Types of Silicate Minerals List: The Most Special Examples

Here is a different types of silicate minerals list where you’ll learn what a silicate mineral is and why they are important. Here there are lists of categories, families, and classes of silicate minerals with their crystal structures.

Overall what makes a mineral a silicate is the presence of silicon-oxygen tetrahedra as the building blocks. Silicate structures on a small scale are very versatile, leading to unique characteristics in every class, subclass, and species of silicate mineral.

In this series on silicates, I focus on the molecular geometry and its effect on characteristics of individual species. Several individual species of silicate mineral are interesting enough to warrant its own post, there are subsequent write-ups on olivine, zeolites and more. This and previous articles continue to build us a framework to understand hysteresis in the Earth’s crust, which only occurs in materials with special magnetic properties. Further, mixed silicate rocks tell researchers about the rock’s formation, since the gradient of different silicates occurs with different temperature and pressure conditions over time.

Why would we care about a different types of silicate minerals list?

Silicates comprise most natural rock. If you are already familiar with the classifications of natural rock as sedimentary, metamorphic, and igneous, know that silicates in general make up a good portion of all three of those designations (over 90% overall).

As far back as the Neolithic era, 10,200 years ago, humans gathered and made use of silicate minerals. The Stone Age civilizations made tools of chalcedony, dried clay for bricks, and beads of aquamarine and lazurite. There are even mention of silicates in passages in the bible, such as:

^15-20 “Now make a Breastpiece of Judgment, using skilled craftsmen [..] Mount four rows of precious gemstones on it.

    First row: carnelian, topaz, emerald.
    Second row: ruby, sapphire, crystal.
    Third row: jacinth, agate, amethyst.
    Fourth row: beryl, onyx, jasper.”

Exodus 28:15-20 (Different versions use different stone names as well.)

“¹⁹And the foundations of the wall of the city were garnished with all manner of precious stones. The first foundation was jasper; the second, sapphire; the third, a chalcedony; the fourth, an emerald; ²⁰ the fifth, sardonyx; the sixth, sardius; the seventh, chrysolite; the eighth, beryl; the ninth, a topaz; the tenth, a chrysoprasus; the eleventh, a jacinth; the twelfth, an amethyst.”

Revelations 21:19-20

Those silicates stayed useful as lapidary and tools. In Greco-Roman times, Theophrastus’s On Stones and Pliny the Elder’s Naturlis Historia mention and describe silicates to the extent of the sciences at the time. The Renaissance through the Scientific Revolution took academic and practical knowledge on silicate minerals from basic classifications of rocks to x-ray diffraction and spectroscopy instruments. Thanks to those newer instruments, we know the finer structures of silicates today.

These structures are really small, on the units of Angstroms, or atomic lengths. One hundred Angstroms is one-billionth of a meter, and one-billionth of a meter is about 1% of a skin cell diameter. Crystallographers discovered these small structures by x-ray crystallography mainly. By reflecting x-rays into a sample at different angles the structure is determined by the spacing between planes. William Bragg’s 1927 article on the structure of silicates first documented different types of silicates by x-ray crystallography.

And silicate minerals are more useful than ever, with applications in technology, construction, and everyday manufacturing.

What qualifies as a mineral?

A mineral in general must be inorganic (never once was a living organism) with a repeating crystal structure.

Glasses, like obsidian, are not minerals although it contains the same elements as minerals. Glasses have random, disorderly structure. Minerals form through natural processes and have a definite chemical formula. The crystal structure of different samples of the same mineral are the same. That’s why composite rocks with visible irregularity like granite are not in themselves minerals but composed of different minerals together.

Coal is not a mineral for example, because it is organic (containing hydrocarbons from deceased organisms.) Diamond contains no hydrocarbons and is therefore an inorganic mineral. And pure elemental metals (copper, gold, etc) are considered minerals.

Examples of different types of silicate minerals:

• Quartz
• Zircon
• Emerald
• Shungite
• Clays
• Topaz
• Beryl
• Tourmaline
• Amythest
• Agate
• Jasper
• Lazurite

Particularly some examples you could be familiar with:

• mica, glittery or sparkly additive in foods, makeup, crafts
• quartz countertops, jewelry and purified glass
• semi-transparent gemstones like garnet, emerald, and zircon
• zeolites and clay in industrial applications like building and fill

Ways to Categorize Different Silicate Minerals

A basic way to categorize silicate minerals is into the two broad categories:

• Ferromagnesian
• Non-ferromagnesian

Ferromagnesian silicates, also called mafic, tend to be darker in color and have inclusions of magnesium and iron (hence the name, with ferro- referring to iron), as well as calcium. Ferromagnesian silicates make up the oceanic crust and mantle.

Non-ferromagnesian silicates, also called felsic, tend to be lighter in color. Their inclusions are commonly sodium, potassium, and aluminum. Non-ferromagnesian silicates make up the majority of continental crust on Earth.

A more specific way to categorize a list of different silicate minerals is based on the structure of how the silicon-oxygen tetrahedra bond to each other.

The classes are:

• Nesosilicates (single islands of tetrahedra, simplest bonding) Si:O is 1:4
• Sorosilicates (paired tetrahedra)
• Inosilicates (chains of tetrahedra)
• Cyclosilicates (rings of tetrahedra)
• Phyllosilicates (sheets of tetrahedra)
• Tectosilicates (cages of tetrahedra, most complex bonding) Si:O is 1:2

Within those categories, some different geometries still arise. For example, inosilicate chained structures can form single chains or double chains. Cyclosilicates may have different numbers of tetrahedra in each ring. The numbers of oxygens shared between tetrahedron make an overall silicon to oxygen ratio that categorizes its geometric structure. Additionally, different positively charged ions can substitute in to balance the negative ion Si_xO_y, so there are many possible features even within subcategories of silicate.

Examples of the exact structure in each of these groups and plenty of examples are in Silicate Types part 2 linked at the end.

A Silly Little Thing Called Silicate

Remember that “silicon” is the element, from the periodic table. A silicon-oxygen tetrahedron is one atom of silicon bonded with four oxygen atoms, SiO₄. A silicate is a mineral made up of silicon-oxygen tetrahedra. (And neither of these has to do with “silicone,” a polymer involving silicon.) Microchips are made from silicon, the pure element, doped with impurities, like phosphorus and boron. Silicate is not really something that you’d want to ingest, but silica (in the form of silicon dioxide) is found in foods like bananas and avocados. In fact, the silica anti-caking “do not eat” packets are non-toxic. The “do not eat” on silica packets is due to a choking hazard.

How Different Silicate Minerals Form

Magmas contain silicon in the form of silica, SiO₂, and form various silicate minerals as it solidifies. Notice this ratio is 1:2. Most silicates have a lower silicon to oxygen ratio, such as nesosilicates at 1:4 and phyllosilicates at 2:5. As magma cools, different silicate minerals can form as those bonds rearrange and blend with other local minerals.

Low amounts of silica ~> dark mafic rock: olivine, pyroxene, ampiboles
High amounts of silica ~> light felsic rock: quartz, feldspar

Example crystallization temperatures:
~1800ºC forsterite (neso-, 1:4 silicon-oxygen ratio)
~1500ºC pyroxene (ino-, 1:3 silicon-oxygen ratio)
~750ºC quartz (tecto-, 1:2 silicon-oxygen ratio)

Remember the cooler temperature formation takes longer to form because the magma starts from a higher temperature then cools. Magma solidifies at just over 1800ºC. More than just temperature and silica content determine what type of silicate will form in the end, like content of other minerals. These trends are accounted for in the Bowen’s reaction series.

The general trend to understand in silicate classes is complexity of silicon-oxygen bonding. Single tetrahedra (neso-, ratio of 1:4) are simpler than cages of tetrahedra (tecto-, ratio of 1:2). As the bonding gets more complex, the silicon to oxygen ratio increases, as there are more oxygen “corners” shared in the network, and a higher percentage of silicon overall. Nature doesn’t actually put minerals into these neat tidy groups. Within a sample, minerals near to each other on the “transformation spectrum” will occur together mixed like superman ice cream. A chunk of random rock like granite has the different categories of silicates mixed within it.

The term “polymerization” also refers to the complexity of the bonding. SiO₄ is the least polymerized, and SiO₂ the most, so all silicates have a silicon to oxygen ratio between 1:4 and 1:2.

Understanding the Puzzle of Different Types of Silicates

The basic building block of a silicate mineral is the silicon-oxygen tetrahedron. Alone, SiO₄ has a charge of -4. The silicon-oxygen tetrahedra make structures by combining with themselves and other, positively charged ions.

Notice that we are balancing Si_xO_y, and not simply SiO₄. Based on how the silicon oxygen tetrahedra are bonded to each other, some of the oxygen “corners” of the tetrahedra are shared, changing the overall ratio of silicon to oxygen as well as the charge of the ions needed to balance it. The positive cations are often metallic elements, like iron, aluminum, or magnesium.

Silicate minerals pattern of structure

Think of silicates as a two part puzzle – the silicon-oxygen tetrahedra and the positive cations that neutralize it. The charges and sizes of ions determine which pieces can fit together.

In an ionic bond, a negative atom and positive atom combine. The negative part is called the anion and this determines the “ates” suffix. Think of other chemical names like “sulfates” or “phosphates”. Sulfur or phosphorus is then in the negative ion (usually with oxygen). So in silicates, a positive ion (cation, like a metal) is bonded with a silicate ion (negative anion).

The first puzzle piece is the negative ion containing silicon – but in some cases aluminum substitutes for silicon in a certain fraction of the spots. The second puzzle piece is the positive cation which is usually a metal, think alkali metals (like sodium, potassium) and/or transition metals (like iron, manganese). Metals can often take a few different cation charges, for example iron is often laying around in both the Fe⁺² and Fe⁺³ states.

Possible crystal structures

The silicon-oxygen tetrahedra are building blocks, but there can be a lot of other “filler” between the backbone of bonded or isolated silicon-oxygen tetrahedra. The positive metal cations bonding directly in the silicon-oxygen tetrahedra backbone balance the charge and energetically stabilize the structure. Between the bonded silicon-oxygen frameworks there could be other crystalline regimes, such as in phyllosilicates, where layers of “sandwich” are found between sheets of silicon-oxygen tetrahedra. The small-scale structures repeat on larger scales so it relates to the shapes the mineral make at larger scale when forming or the natural cleavage plane when the rock is cut (known as the correspondence principle).

The elements present between the silicon-oxygen tetrahedra depend on what elements are present under the high-temperature, high-pressure, formation conditions.

In each group the important characteristics are

• what cations are in between the tetrahedra
• what shape the tetrahedra make on their own
• the ratio of silicon to oxygen as a result of the tetrahedra bonding to each other

The variation give silicate minerals a variety of physical properties, like ability to conduct electricity.

Ever-transitioning Rocks “Series” and “Endmembers”

Over temperature and pressure, the shape of the spaces available for cations changes. Similar-sized ions of the same charge swap out and give information about how much pressure over time a sample rock has experienced. Geologists use charts with element possibilities on the axes and a polygon to show the extremities of what can form. In simpler cases, like the forsterite (Mg₂SiO₄) to fayalite (Fe₂SiO₄) transition (nesosilicates), the series is more like a straight line as Mg swaps out to Fe. In silicates like amphiboles where there’s two different cation “slots” that can swap out, the transition series is expressed in a quadrilateral diagram. (Examples in part 2.)

Understanding the Chemical Formulas for Silicates

Remember the silicon-oxygen tetrahedron is SiO₄^4-, but when some of the oxygen corners of the tetrahedra are shared, the ratio of silicon to oxygen becomes higher than 1:4. This also changes the charge and therefore the types of positive ions that it stably bonds with. There are 2 parts:

• the cations, all the “other” distinguishing elements that can often swap out
• the silicate part, Si_xO_y, the x and y numbers coming from how many oxygens the bonded tetrahedra share

In most silicates, we have the cation, the positively-charged part, the first part of the chemical formula with a pantry of different elemental substitution options. Then we have the negatively-charged silicate part. When aluminum substitutes for silicon, that is specified in the slot where silicon is in the silicate chemical formula. Sometimes the ratios of silicate to aluminum or the ratios of different cations are specified as a range of possibilities to describe a group. For example, the inosilicate subclass clinopyroxenes has a formula Ca(Mg,Fe)Si₂O₆, indicating Mg OR Fe. The cations that will bond to this will even out the negative charge.

Next is looking at each of the six silicate types by structure, and we’ll see how the tetrahedra actually arrange on a smaller-than-microscopic scale!

~~>Click here for part 2, going through each of the silicate types (when it’s clickable)