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Tectosilicate Introduction

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Tectosilicate, also known as framework silicate, is any element of a group of compounds having a structure that has silicate tetrahedrons(each of which includes central silicon atoms surrounded by four oxygen atoms at the corners of a tetrahedron). Each of the four oxygen atoms of a given tetrahedron is joined with another tetrahedron. Each tetrahedron is further connected to four others. Tectosilicate, along with the quartz and other silicate minerals having a chemical formula consisting of some multiples of SiO₂.

What is Tectosilicate?

Tectosilicate or Framework silicate is the substantial group of silicates consisting of approximately 75% of the earth's crust. Framework silicates are identified by the three-dimensional structure of silica tetrahedra. Tectosilicate examples are the members of the quartz, feldspar, and zeolite group of minerals. Excluding the quartz group, they are considered as aluminosilicates with the general chemical formula AlXSiyO2(x + y))x-(1:2 ratio of Si to O atoms). 

The tectosilicate can include extra cations if some of the silicates are substituted by additional lower charge cations such as aluminum to give an overall negative charge. This replacement can also occur in other forms of silicates.

Some sparse minerals may consist of more than one type of anion coinciding in their crystal structure, or they may include complex anions that are halfway between the types written above.

Tectosilicate Definition

Tectosilicate is defined as the polymeric silicates in which silicon oxygen tetrahedral groups are correlated by splitting all their oxygen atoms with other groups so as to form three dimensional structure or network.

Tectosilicate  Fórmula

The general formula of three-dimensional or tectosilicate or framework silicate is (SiO₂)n. All the oxygen atoms of Si04 are united with other tetrahedra and hence forming the three dimensional network.

Eg SiO₂- quartz, tridymite, cristobalite- These oxide minerals are the crystallized form of silica. 

Three-dimensional  aluminosilicates are formed when Sio44- gets replaced with AlO45-.

Eg. Feldspar, zeolites  and Ult etc.

Tectosilicate Structure

Tectosilicate structure is made up of interconnected tetrahedra moving externally in all directions forming an intricate framework. All the oxygen is combined with other tetrahedra in the lower groups. In the nearly pure form of oxygen and silicon, the most predominant mineral found is quartz(SiO2). 

Aluminum can easily be substituted for the silicon ion in the tetrahedron. In other classes, this occurs to a certain degree but it is the biggest factor of the diversified structure. 

While tetrahedron is approximately the same as aluminum at its center, the charge is now a negative (-5) instead of a negative (-4). As the charge in a crystal must be balanced, additional cations are required in the tectosilicate structure and this is the basic reason for the maximum variations in the lower groups.

Tectosilicate Examples

The tectosilicate group includes the most abundant minerals composing the Earth crust. These includes

Quartz - 12%

Plagioclase Feldspar - 39%

Orthoclase Feldspar - 12%

Some Tectosilicate Examples Include: 

Orthoclase - KALSi₃O₈

Anorthite - CaAl₂Si₂O₈

Labradorite - (Ca, Na)(Al, Si)₄O₈

Albite - NaAlSi₃O₈

Quartz - SiO2

Did You Know?

  • Tectosilicate is a group of silicates that consists of all four oxygen atoms from each tetrahedron sharing themselves.

  • The tectosilicates that contain Al are commonly known as plagioclase or feldspar.

  • Feldspar is the name of the group of rocks forming tectosilicate minerals that comprise as much as 60% of the Earth's crust.

  • Tectosilicates represent almost 60% of the rock crust of the Earth. The Silicate group and feldspar group are the two most important groups.

FAQ (Frequently Asked Questions)

1. What are Silicate Minerals?

Ans: Silicate minerals are rock-forming minerals consisting of silicate groups. Silicate minerals are the largest and the most important part class of minerals and make up approximately 90% of Earth's crust. In mineralogy, silica dioxide is usually considered a silicate mineral. In nature, the Silica is detected as the mineral quartz and its polymorphs.

2. What is the Hardness of Tectosilicate?

Ans: The Framework Silicate or tectosilicate having a structure wherein all the oxygen of Sio4 tetrahedra is shared with another tetrahedron. The ratio of Sio2 to O is hence 1:2.

As the Si bonds are strong covalent bonds and since the structure is interlocking, the tectosilicate or framework silicates tend to have high hardness.

3. Is Feldspar a Tectosilicate?

Ans: Yes, feldspar is a category of rocks forming tectosilicate minerals that makeup about 41% of the Earth's continental crust by weight. This group of minerals consists of tectosilicates, silicate minerals in which silicate ions are interconnected by shared oxygen ions to form three dimensional networks.