How can you tell glass from quartz?

Qualitative scale characterizing scratch resistance

Mohs hardness kit, containing one specimen of each mineral on the ten-point hardness scale

The Mohs scale of mineral hardness ( ) is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of minerals through the ability of harder material to scratch softer material.

The scale was introduced in 1812 by the German geologist and mineralogist Friedrich Mohs, in his book "Versuch einer Elementar-Methode zur naturhistorischen Bestimmung und Erkennung der Fossilien";[1][2] it is one of several definitions of hardness in materials science, some of which are more quantitative.[3]

The method of comparing hardness by observing which minerals can scratch others is of great antiquity, having been mentioned by Theophrastus in his treatise On Stones, c. 300 BC, followed by Pliny the Elder in his Naturalis Historia, c. AD 77.[4][5][6] The Mohs scale is useful for identification of minerals in the field, but is not an accurate predictor of how well materials endure in an industrial setting.[7]

Reference minerals

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The Mohs scale of mineral hardness is based on the ability of one natural sample of mineral to scratch another mineral visibly. The samples of matter used by Mohs are all different minerals. Minerals are chemically pure solids found in nature. Rocks are made up of one or more minerals. As the hardest known naturally occurring substance when the scale was designed, diamonds are at the top of the scale. The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, or the softest material that can scratch the given material. For example, if some material is scratched by apatite but not by fluorite, its hardness on the Mohs scale would be between 4 and 5.[8]

"Scratching" a material for the purposes of the Mohs scale means creating non-elastic dislocations visible to the naked eye. Frequently, materials that are lower on the Mohs scale can create microscopic, non-elastic dislocations on materials that have a higher Mohs number. While these microscopic dislocations are permanent and sometimes detrimental to the harder material's structural integrity, they are not considered "scratches" for the determination of a Mohs scale number.[9]

Each of the ten hardness values in the Mohs scale is represented by a reference mineral, most of which are widespread in rocks.

The Mohs scale is an ordinal scale. For example, corundum (9) is twice as hard as topaz (8), but diamond (10) is four times as hard as corundum. The table below shows the comparison with the absolute hardness measured by a sclerometer, with pictorial examples.[10][11]

Mohs hardness Reference mineral Chemical formula Absolute hardness[12] Image 1 Talc Mg3Si4O10(OH)2 1 2 Gypsum CaSO4·2H2O 2 3 Calcite CaCO3 14 4 Fluorite CaF2 21 5 Apatite Ca5(PO4)3(OH−,Cl−,F−) 48 6 Orthoclase feldspar KAlSi3O8 72 7 Quartz SiO2 100 8 Topaz Al2SiO4(OH−,F−)2 200 9 Corundum Al2O3 400 10 Diamond C 1500

Examples

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Below is a table of more materials by Mohs scale. Some of them have a hardness between two of the Mohs scale reference minerals. Some solid substances which are not minerals have been assigned a hardness on the Mohs scale. However, if the substance is actually a mixture of other substances, hardness can be difficult to determine or may be misleading or meaningless. For example, some sources have assigned a Mohs hardness of 6 or 7 to granite but it is a rock made of several minerals, each with its own Mohs hardness (e.g. topaz-rich granite contains: topaz - hardness 8, quartz - hardness 7, orthoclase feldspar - hardness 6, plagioclase feldspar - hardness 6 to 6.5, mica - hardness 2 to 4).

Use

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Despite its lack of precision, the Mohs scale is relevant for field geologists, who use the scale to roughly identify minerals using scratch kits. The Mohs scale hardness of minerals can be commonly found in reference sheets.

Mohs hardness is useful in milling. It allows assessment of which type of mill and grinding medium will best reduce a given product whose hardness is known.[20]

The scale is used by electronic manufacturers for testing the resilience of flat panel display components (such as cover glass for LCDs or encapsulation for OLEDs), as well as to evaluate the hardness of touch screens in consumer electronics.[21]

Comparison with Vickers scale

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Comparison between Mohs hardness and Vickers hardness:[22]

Mineral
name Hardness (Mohs) Hardness (Vickers)
(kg/mm2) Tin 1.5 VHN10 = 7–9 Bismuth 2–2.5 VHN100 = 16–18 Gold 2.5 VHN10 = 30–34 Silver 2.5 VHN100 = 61–65 Chalcocite 2.5–3 VHN100 = 84–87 Copper 2.5–3 VHN100 = 77–99 Galena 2.5 VHN100 = 79–104 Sphalerite 3.5–4 VHN100 = 208–224 Heazlewoodite 4 VHN100 = 230–254 Goethite 5–5.5 VHN100 = 667 Chromite 5.5 VHN100 = 1,278–1,456 Anatase 5.5–6 VHN100 = 616–698 Rutile 6–6.5 VHN100 = 894–974 Pyrite 6–6.5 VHN100 = 1,505–1,520 Bowieite 7 VHN100 = 858–1,288 Euclase 7.5 VHN100 = 1,310 Chromium 8.5 VHN100 = 1,875–2,000

See also

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References

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Further reading

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With the continuous rapid development of society, the types of glass are becoming more and more diverse, which can meet the needs of various occasions. After adjusting its materials and properties, glass materials can undergo different changes, making it more stable and durable. Let's take a look at the differences between quartz glass and regular glass together.

1. Different hardness

The hardness of the former can generally reach Mohs level seven, while the hardness of the latter can generally only reach levels 5.5 to 6.

2. Different light transmittance

The former can pass through infrared and ultraviolet rays, while the latter cannot.

3. Different colors

The former generally has no color, while the latter generally has a certain color.

4. Different high temperature resistance

        After the former is burned red, even if it is immediately placed in water, it is not easy to crack, while once the latter is burned, it will immediately crack.

The difference between quartz glass and ordinary glass: quartz is crystal and glass is amorphous solid.

1. The main components of ordinary glass are sodium silicate, silicon dioxide, and calcium silicate, while the main component of quartz glass is silicon dioxide.

2. The content of silica varies. Quartz glass is made by melting pure silica, with a content of over 99%. The silicon dioxide content of ordinary glass is generally between 70% -75%, and other components are alkali metals or alkaline earth metals such as sodium oxide and calcium oxide, in order to reduce melting temperature and improve material properties.

3. Quartz is a mineral composed of silicon dioxide, with the chemical formula SiO2. Pure quartz is colorless and transparent, and appears in various colors due to the presence of trace pigment ions, finely dispersed inclusions, or color centers, which reduces transparency. It has a glassy luster, and the fracture surface has a greasy luster. Hardness 7, no cleavage, conchoidal fracture, specific gravity 2.65, piezoelectricity.

   

Quartz is one of the minerals widely distributed on the earth's surface. There are many types of quartz. Vein quartz, quartz sand, quartzite, sandstone, silica, opal, diatomite, etc. are used as raw materials for daily ceramics. It is a substance homologous to ordinary sand and crystal.

Glass is an amorphous inorganic non-metallic material, which is generally made of a variety of inorganic minerals (such as quartz sand, borax, boric acid, barite, barium carbonate, limestone, feldspar, soda ash, etc.) as the main raw materials, and a small amount of auxiliary raw materials are added. Its main components are silicon dioxide and other oxides. The chemical composition of ordinary glass is Na2SiO3, CaSiO3, SiO2 or Na2O · CaO · 6SiO2, etc. The main component is silicate double salt, which is an amorphous solid with an irregular structure. Widely used in buildings for wind and light insulation, it belongs to mixtures. There are also colored glass mixed with oxides or salts of certain metals to show color, and tempered glass made through physical or chemical methods.

The simple classification of glass is mainly divided into flat glass and deep processed glass. Plate glass is mainly divided into three types: pull-up plate glass (divided into slotted and non slotted types), flat pull plate glass, and float glass. Due to its uniform thickness, flat and parallel upper and lower surfaces, as well as factors such as high labor productivity and easy management, float glass is becoming the mainstream of glass manufacturing methods.