earth science

Silicate mineral

Silicate mineral is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Silicate mineral rather than just read about it. In short: Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust.

Key takeaways

Silicate mineral belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Silicate mineral to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Silicate mineral from memory before moving on to harder problems.

Reference excerpt

Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (SiO2) are usually considered to be tectosilicates, and they are classified as such in the Dana classification system (75.1). However, the Nickel–Strunz classification categorizes them as oxide minerals (4.DA). Silica is found in nature as the mineral quartz and its polymorphs. On Earth, a wide variety of silicate minerals occur in an even wider range of combinations as a result of the processes that have been forming and re-working the crust for billions of years. These processes include partial melting, crystallization, fractionation, metamorphism, weathering, and diagenesis.

Living organisms also contribute to this geologic cycle. For example, a type of plankton known as diatoms construct their exoskeletons ("frustules") from silica extracted from seawater. The frustules of dead diatoms are a major constituent of deep ocean sediment, and of diatomaceous earth.

General structure A silicate mineral is generally an inorganic compound consisting of subunits with the formula [SiO2+n]2n−. Although depicted as such, the description of silicates as anions is a simplification. Balancing the charges of the silicate anions are metal cations, Mx+. Typical cations are Mg2+, Fe2+, and Na+. The Si-O-M linkage between the silicates and the metals are strong, polar-covalent bonds. Silicate anions ([SiO2+n]2n−) are invariably colorless, or when crushed to a fine powder, white. The colors of silicate minerals arise from the metal component, commonly iron. In most silicate minerals, silicon is tetrahedral, being surrounded by four oxides. The coordination number of the oxides is variable except when it bridges two silicon centers, in which case the oxide has a coordination number of two. Some silicon centers may be replaced by atoms of other elements, still bound to the four corner oxygen corners. If the substituted atom is not normally tetravalent, it usually contributes extra charge to the anion, which then requires extra cations. For example, in the mineral orthoclase [KAlSi3O8]n, the anion is a tridimensional network of tetrahedra in which all oxygen corners are shared. If all tetrahedra had silicon centers, the anion would be just neutral silica [SiO2]n. Replacement of one in every four silicon atoms by an aluminum atom results in the anion [AlSi3O−8]n, whose charge is neutralized by the potassium cations K+.

Main groups In mineralogy, silicate minerals are classified into seven major groups according to the structure of their silicate anion:

Tectosilicates can only have additional cations if some of the silicon is replaced by an atom of lower valence such as aluminum. Al for Si substitution is common.

Nesosilicates or orthosilicates

Nesosilicates (from Greek νῆσος nēsos 'island'), or orthosilicates, have the orthosilicate ion, present as isolated (insular) [SiO4]4− tetrahedra connected only by interstitial cations. The Nickel–Strunz classification is 09.A –examples include:

Phenakite – Be2SiO4 Willemite – Zn2SiO4 Olivine group Forsterite – Mg2SiO4 Fayalite – Fe2SiO4 Tephroite – Mn2SiO4 Garnet group Pyrope – Mg3Al2(SiO4)3 Almandine – Fe3Al2(SiO4)3 Spessartine – Mn3Al2(SiO4)3 Grossular – Ca3Al2(SiO4)3 Andradite – Ca3Fe2(SiO4)3 Uvarovite – Ca3Cr2(SiO4)3 Hydrogrossular – Ca3Al2Si2O8(SiO4)3−m(OH)4m Zircon group Zircon – ZrSiO4 Thorite – (Th,U)SiO4 Hafnon – (Hf,Zr)SiO4 Wollastonite group (pyroxenoid group) Wollastonite – CaSiO₃ Pectolite – NaCa₂Si₃O₈(OH) Serandite – Na(Mn²⁺,Ca)₂Si₃O₈(OH) Nambulite – LiMn₄Si₅O₁₄(OH) Fowlerite – (Ca,Mn)₂Si₃O₈(OH)

Al2SiO5 group Andalusite – Al2SiO5 Kyanite – Al2SiO5 Sillimanite – Al2SiO5 Dumortierite – Al6.5–7BO3(SiO4)3(O,OH)3 Topaz – Al2SiO4(F,OH)2 Staurolite – Fe2Al9(SiO4)4(O,OH)2 Humite group – (Mg,Fe)7(SiO4)3(F,OH)2 Norbergite – Mg3(SiO4)(F,OH)2 Chondrodite – Mg5(SiO4)2(F,OH)2 Humite – Mg7(SiO4)3(F,OH)2 Clinohumite – Mg9(SiO4)4(F,OH)2 Datolite – CaBSiO4(OH) Titanite – CaTiSiO5 Chloritoid – (Fe,Mg,Mn)2Al4Si2O10(OH)4 Mullite (aka Porcelainite) – Al6Si2O13

Sorosilicates

Sorosilicates (from Greek σωρός sōros 'heap, mound') have isolated pyrosilicate anions Si2O6−7, consisting of double tetrahedra with a shared oxygen vertex—a silicon:oxygen ratio of 2:7. The Nickel–Strunz classification is 09.B. Examples include:

Thortveitite – (Sc,Y)2(Si2O7) Hemimorphite (calamine) – Zn4(Si2O7)(OH)2·H2O Lawsonite – CaAl2(Si2O7)(OH)2·H2O Axinite – (Ca,Fe,Mn)3Al2(BO3)(Si4O12)(OH) Ilvaite – CaFeII2FeIIIO(Si2O7)(OH) Epidote group (has both (SiO4)4− and (Si2O7)6− groups} Epidote – Ca2(Al,Fe)3O(SiO4)(Si2O7)(OH) Zoisite – Ca2Al3O(SiO4)(Si2O7)(OH) Tanzanite – Ca2Al3O(SiO4)(Si2O7)(OH) Clinozoisite – Ca2Al3O(SiO4)(Si2O7)(OH) Allanite – Ca(Ce,La,Y,Ca)Al2(FeII,FeIII)O(SiO4)(Si2O7)(OH) Dollaseite-(Ce) – CaCeMg2AlSi3O11F(OH) Vesuvianite (idocrase) – Ca10(Mg,Fe)2Al4(SiO4)5(Si2O7)2(OH)4

Cyclosilicates

Cyclosilicates (from Greek κύκλος kýklos 'circle'), or ring silicates, have three or more tetrahedra linked in a ring. The general formula is (SixO3x)2x−, where one or more silicon atoms can be replaced by other 4-coordinated atom(s). The silicon:oxygen ratio is 1:3. Double rings have the formula (Si2xO5x)2x− or a 2:5 ratio. The Nickel–Strunz classification is 09.C. Possible ring sizes include:

Some example minerals are:

3-member single ring Benitoite – BaTi(Si3O9) 4-member single ring Papagoite – CaCuAlSi2O6(OH)3. 6-member single ring Beryl – Be3Al2(Si6O18) Bazzite – Be3Sc2(Si6O18) Sugilite – KNa2(Fe,Mn,Al)2Li3Si12O30 Tourmaline – (Na,Ca)(Al,Li,Mg)3–(Al,Fe,Mn)6(Si6O18)(BO3)3(OH)4 Pezzottaite – Cs(Be2Li)Al2Si6O18 Osumilite – (K,Na)(Fe,Mg)2(Al,Fe)3(Si,Al)12O30 Cordierite – (Mg,Fe)2Al4Si5O18 Sekaninaite – (Fe+2,Mg)2Al4Si5O18 9-member single ring Eudialyte – Na15Ca6(Fe,Mn)3Zr3SiO(O,OH,H2O)3(Si3O9)2(Si9O27)2(OH,Cl)2 6-member double ring Milarite – K2Ca4Al2Be4(Si24O60)H2O The ring in axinite contains two B and four Si tetrahedra and is highly distorted compared to the other 6-member ring cyclosilicates.

Inosilicates

Inosilicates (from Greek ἴς is [genitive: ἰνός inos] 'fibre'), or chain silicates, have interlocking chains of silicate tetrahedra with either SiO3, 1:3 ratio, for single chains or Si4O11, 4:11 ratio, for double chains. The Nickel–Strunz classification is 09.D – examples include:

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Silicate mineral

Start with the simplest possible case. Write down what Silicate mineral claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Silicate mineral before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Silicate mineral ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Silicate mineral

In research: Silicate mineral appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Silicate mineral in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Silicate mineral is common in secondary-school and first-year university syllabi. It links to neighbouring topics Silicate minerals, so understanding it makes those chapters shorter.
In everyday life: Look for Silicate mineral outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Silicate mineral in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Silicate mineral means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Silicate mineral out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Silicate mineral in simple terms?

Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust.

Why does Silicate mineral matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Silicate mineral?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Silicate mineral.