Editing Mineral (section)

==Physical properties==
Classifying minerals ranges from simple to difficult. A mineral can be identified by several physical properties, some of them being sufficient for full identification without equivocation. In other cases, minerals can only be classified by more complex [[Optical mineralogy|optical]], [[Analytical chemistry|chemical]] or [[X-ray diffraction]] analysis; these methods, however, can be costly and time-consuming.  Physical properties applied for classification include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, cleavage and fracture, and specific gravity. Other less general tests include [[fluorescence]], [[phosphorescence]], [[magnetism]], [[radioactivity]], tenacity (response to mechanical induced changes of shape or form), [[piezoelectricity]] and reactivity to dilute [[acid]]s.<ref>{{harvnb|Dyar|Gunter|2008}}, pp. 22–23</ref>

===Crystal structure and habit===
<!--[[File:Natroliteinde1.jpg|Acicular [[natrolite]]|right|thumb]]-->
{{main article|Crystal system|Crystal habit}}
{{see also|Crystal twinning}}
<!-- distinguish /habit/ and /structure/. Discuss crystal systems. -->
[[File:Topaz-235220.jpg|right|thumb|[[Topaz]] has a characteristic orthorhombic elongated crystal shape.]]
[[Crystal structure]] results from the orderly geometric spatial arrangement of atoms in the internal structure of a mineral. This crystal structure is based on regular internal atomic or [[ion]]ic arrangement that is often expressed in the geometric form that the crystal takes. Even when the mineral grains are too small to see or are irregularly shaped, the underlying crystal structure is always periodic and can be determined by [[X-ray]] diffraction.<ref name="DG2_4" /> Minerals are typically described by their symmetry content. Crystals are [[crystallographic restriction theorem|restricted]] to [[Crystallographic point group|32 point groups]], which differ by their symmetry. These groups are classified in turn into more broad categories, the most encompassing of these being the six crystal families.<ref name="DG69-80">{{harvnb|Dyar|Gunter|2008}}, pp. 69–80</ref>

These families can be described by the relative lengths of the three crystallographic axes, and the angles between them; these relationships correspond to the symmetry operations that define the narrower point groups. They are summarized below; a, b, and c represent the axes, and α, β, γ represent the angle opposite the respective crystallographic axis (e.g. α is the angle opposite the a-axis, [[wikt:viz.|viz.]] the angle between the b and c axes):<ref name="DG69-80" />

{| class="wikitable"
|-
!Crystal family
!Lengths
!Angles
!Common examples
|-
|[[Cubic crystal system|Isometric]]
|a = b = c
|α = β = γ = 90°
|[[Garnet]], [[halite]], [[pyrite]]
|-
|[[Tetragonal]]
|a = b ≠ c
|α = β = γ = 90°
|[[Rutile]], [[zircon]], [[andalusite]]
|-
|[[Orthorhombic]]
|a ≠ b ≠ c
|α = β = γ = 90°
|[[Olivine]], [[aragonite]], [[orthopyroxene]]s
|-
|[[Hexagonal crystal system|Hexagonal]]
|a = b ≠ c
|α = β = 90°, γ = 120°
|[[Quartz]], [[calcite]], [[tourmaline]]
|-
|[[Monoclinic]]
|a ≠ b ≠ c
|α = γ = 90°, β ≠ 90°
|[[Clinopyroxene]]s, [[orthoclase]], [[gypsum]]
|-
|[[Triclinic]]
|a ≠ b ≠ c
|α ≠ β ≠ γ ≠ 90°
|[[Anorthite]], [[albite]], [[kyanite]]
|}

The hexagonal crystal family is also split into two crystal ''systems''&nbsp;– the [[trigonal]], which has a three-fold axis of symmetry, and the hexagonal, which has a six-fold axis of symmetry.

Chemistry and crystal structure together define a mineral. With a restriction to 32 point groups, minerals of different chemistry may have identical crystal structure. For example, [[halite]] (NaCl), [[galena]] (PbS), and [[periclase]] (MgO) all belong to the hexaoctahedral point group (isometric family), as they have a similar [[stoichiometry]] between their different constituent elements. In contrast, [[Polymorphism (materials science)|polymorphs]] are groupings of minerals that share a chemical formula but have a different structure. For example, [[pyrite]] and [[marcasite]], both iron sulfides, have the formula FeS<sub>2</sub>; however, the former is isometric while the latter is orthorhombic. This polymorphism extends to other sulfides with the generic AX<sub>2</sub> formula; these two groups are collectively known as the pyrite and marcasite groups.<ref>{{harvnb|Dyar|Gunter|2008}}, pp. 654–55</ref>

Polymorphism can extend beyond pure symmetry content. The aluminosilicates are a group of three minerals&nbsp;– [[kyanite]], [[andalusite]], and [[sillimanite]]&nbsp;– which share the chemical formula Al<sub>2</sub>SiO<sub>5</sub>. Kyanite is triclinic, while andalusite and sillimanite are both orthorhombic and belong to the dipyramidal point group. These differences arise corresponding to how aluminium is coordinated within the crystal structure. In all minerals, one aluminium ion is always in six-fold coordination with oxygen. Silicon, as a general rule, is in four-fold coordination in all minerals; an exception is a case like [[stishovite]] (SiO<sub>2</sub>, an ultra-high pressure quartz polymorph with rutile structure).<ref>{{harvnb|Dyar|Gunter|2008}}, p. 581</ref> In kyanite, the second aluminium is in six-fold coordination; its chemical formula can be expressed as Al<sup>[6]</sup>Al<sup>[6]</sup>SiO<sub>5</sub>, to reflect its crystal structure. Andalusite has the second aluminium in five-fold coordination (Al<sup>[6]</sup>Al<sup>[5]</sup>SiO<sub>5</sub>) and sillimanite has it in four-fold coordination (Al<sup>[6]</sup>Al<sup>[4]</sup>SiO<sub>5</sub>).<ref>{{harvnb|Dyar|Gunter|2008}}, pp. 631–32</ref>

Differences in crystal structure and chemistry greatly influence other physical properties of the mineral. The carbon allotropes [[diamond]] and [[graphite]] have vastly different properties; diamond is the hardest natural substance, has an adamantine lustre, and belongs to the isometric crystal family, whereas graphite is very soft, has a greasy lustre, and crystallises in the hexagonal family. This difference is accounted for by differences in bonding. In diamond, the carbons are in sp<sup>3</sup> hybrid orbitals, which means they form a framework where each carbon is covalently bonded to four neighbours in a tetrahedral fashion; on the other hand, graphite is composed of sheets of carbons in sp<sup>2</sup> hybrid orbitals, where each carbon is bonded covalently to only three others. These sheets are held together by much weaker [[van der Waals force]]s, and this discrepancy translates to large macroscopic differences.<ref>{{harvnb|Dyar|Gunter|2008}}, p. 166</ref>

[[File:Spinel-4mb4c.jpg|Contact twins, as seen in [[spinel]]|left|thumb]]

[[Crystal twinning|Twinning]] is the intergrowth of two or more crystals of a single mineral species. The geometry of the twinning is controlled by the mineral's symmetry. As a result, there are several types of twins, including contact twins, reticulated twins, geniculated twins, penetration twins, cyclic twins, and polysynthetic twins. Contact, or simple twins, consist of two crystals joined at a plane; this type of twinning is common in spinel. Reticulated twins, common in rutile, are interlocking crystals resembling netting. Geniculated twins have a bend in the middle that is caused by start of the twin. Penetration twins consist of two single crystals that have grown into each other; examples of this twinning include cross-shaped [[staurolite]] twins and Carlsbad twinning in orthoclase. Cyclic twins are caused by repeated twinning around a rotation axis. This type of twinning occurs around three, four, five, six, or eight-fold axes, and the corresponding patterns are called threelings, fourlings, [[fiveling]]s, sixlings, and eightlings. Sixlings are common in aragonite. Polysynthetic twins are similar to cyclic twins through the presence of repetitive twinning; however, instead of occurring around a rotational axis, polysynthetic twinning occurs along parallel planes, usually on a microscopic scale.<ref name="DG4143">{{harvnb|Dyar|Gunter|2008}}, pp. 41–43</ref><ref>{{harvnb|Chesterman|Lowe|2008}}, p. 39</ref>

Crystal habit refers to the overall shape of the aggregate crystal of any mineral. Several terms are used to describe this property. Common habits include [[acicular (crystal habit)|acicular]], which describes needle-like crystals as in [[natrolite]]; dendritic (tree-pattern) is common in [[native copper]] or [[Gold|native gold]] with a [[Matrix (geology)|groundmass (matrix)]]; equant, which is typical of [[garnet]]; [[prism (geology)|prismatic]] (elongated in one direction) as seen in [[Spodumene|kunzite]] or [[stibnite]]; [[botryoidal]] (like a bunch of grapes) seen in [[chalcedony]]; fibrous, which has fibre-like crystals as seen in [[wollastonite]]; tabular, which differs from bladed habit in that the former is platy whereas the latter has a defined elongation as seen in [[muscovite]]; and massive, which has no definite shape as seen in [[carnallite]].<ref name=2112.d/> Related to crystal form, the quality of crystal faces is diagnostic of some minerals, especially with a petrographic microscope. Euhedral crystals have a defined external shape, while anhedral crystals do not; those intermediate forms are termed subhedral.<ref>{{harvnb|Dyar|Gunter|2008}}, pp. 32–39</ref><ref>{{harvnb|Chesterman|Lowe|2008}}, p. 38</ref>

===Hardness===
{{main article|Mohs scale of mineral hardness}}
[[File:Rough diamond.jpg|right|thumb|Diamond is the hardest natural material, and has a Mohs hardness of 10.]]
The hardness of a mineral defines how much it can resist scratching or indentation. This physical property is controlled by the chemical composition and crystalline structure of a mineral. 

The most commonly used scale of measurement is the [[Ordinal data|ordinal]] Mohs hardness scale, which measures resistance to scratching. Defined by ten indicators, a mineral with a higher index scratches those below it. The scale ranges from talc, a [[phyllosilicate]], to diamond, a carbon polymorph that is the hardest natural material. The scale is provided below:<ref name="DG2829"/><ref name=2112.d/>

{| class="wikitable sortable"
|-
!Mohs hardness
!Mineral
!Chemical formulae
|-
|1
|[[Talc]]
|Mg<sub>3</sub>Si<sub>4</sub>O<sub>10</sub>(OH)<sub>2</sub>
|-
|2
|[[Gypsum]]
|CaSO<sub>4</sub>·2H<sub>2</sub>O
|-
|3
|[[Calcite]]
|CaCO<sub>3</sub>
|-
|4
|[[Fluorite]]
|CaF<sub>2</sub>
|-
|5
|[[Apatite]]
|Ca<sub>5</sub>(PO<sub>4</sub>)<sub>3</sub>(OH,Cl,F)
|-
|6
|[[Orthoclase]]
|KAlSi<sub>3</sub>O<sub>8</sub>
|-
|7
|[[Quartz]]
|SiO<sub>2</sub>
|-
|8
|[[Topaz]]
|Al<sub>2</sub>SiO<sub>4</sub>(OH,F)<sub>2</sub>
|-
|9
|[[Corundum]]
|Al<sub>2</sub>O<sub>3</sub>
|-
|10
|[[Diamond]]
|C
|}
[[File:Mohs-Hardness-Graph.svg|Mohs Scale versus Absolute Hardness|right|frameless]]
A mineral's hardness is a function of its structure. Hardness is not necessarily constant for all crystallographic directions; crystallographic weakness renders some directions softer than others.<ref name="DG2829">{{harvnb|Dyar|Gunter|2008}}, pp. 28–29</ref> An example of this hardness variability exists in kyanite, which has a Mohs hardness of 5{{frac|1|2}} parallel to [[Miller index|[001]]] but 7 parallel to [[Miller index|[100]]].<ref name="Kyanite">{{cite web|url=https://www.mindat.org/min-2303.html|title=Kyanite|access-date=3 April 2018|publisher=[[Mindat.org]]|archive-date=14 September 2019|archive-url=https://web.archive.org/web/20190914132555/https://www.mindat.org/min-2303.html|url-status=live}}</ref>

Other scales include these;<ref>{{cite web |title=Hardness: Vickers, Rockwell, Brinell, Mohs, Shore and Knoop - Matmatch |url=https://matmatch.com/learn/process/hardness-comparison |website=matmatch.com |access-date=4 October 2021 |archive-date=4 October 2021 |archive-url=https://web.archive.org/web/20211004171353/https://matmatch.com/learn/process/hardness-comparison |url-status=live }}</ref>
*[[Shore durometer|Shore's hardness test]], which measures the endurance of a mineral based on the indentation of a spring-loaded contraption.<ref>{{cite web |title=Hardness |url=http://www.calce.umd.edu/general/Facilities/Hardness_ad_.htm#3.5 |access-date=4 October 2021 |date=7 July 2007|archive-url=https://web.archive.org/web/20070707141201/http://www.calce.umd.edu/general/Facilities/Hardness_ad_.htm#3.5 |archive-date=2007-07-07 }}</ref>
*The [[Rockwell scale]]
*The [[Vickers hardness test]]
*The [[Brinell scale]]

===Lustre and diaphaneity===
{{main article|Lustre (mineralogy)}}
[[File:Pyrite 2.jpg|left|thumb|[[Pyrite]] has a metallic lustre.]]
Lustre indicates how light reflects from the mineral's surface, with regards to its quality and intensity. There are numerous qualitative terms used to describe this property, which are split into metallic and non-metallic categories. Metallic and sub-metallic minerals have high reflectivity like metal; examples of minerals with this lustre are [[galena]] and pyrite. Non-metallic lustres include: adamantine, such as in [[diamond]]; vitreous, which is a glassy lustre very common in silicate minerals; pearly, such as in [[talc]] and [[apophyllite]]; resinous, such as members of the garnet group; silky which is common in fibrous minerals such as asbestiform [[chrysotile]].<ref name="DG2628">Dyar and Darby, pp. 26–28</ref>

The [[diaphaneity]] of a mineral describes the ability of light to pass through it. Transparent minerals do not diminish the intensity of light passing through them. An example of a transparent mineral is [[muscovite]] (potassium mica); some varieties are sufficiently clear to have been used for windows. Translucent minerals allow some light to pass, but less than those that are transparent. [[Jadeite]] and [[nephrite]] (mineral forms of [[jade]] are examples of minerals with this property). Minerals that do not allow light to pass are called opaque.<ref name="B72" /><ref name="DG25">{{harvnb|Dyar|Gunter|2008}}, p. 25</ref>

The diaphaneity of a mineral depends on the thickness of the sample. When a mineral is sufficiently thin (e.g., in a [[thin section]] for [[petrography]]), it may become transparent even if that property is not seen in a hand sample. In contrast, some minerals, such as [[hematite]] or pyrite, are opaque even in thin-section.<ref name="DG25" />

===Colour and streak===
{{main article|Streak (mineralogy)}}
{{multiple image
| align = right
| image1 = Quartz-Uvarovite-LTH15C.JPG
| width1 = 150
| alt1 =
| caption1 =
| image2 = Grossular-ww51a.jpg
| width2 = 161
| alt2 =
| caption2 =
| footer = Colour is typically not a diagnostic property of minerals. Shown are green [[uvarovite]] (left) and red-pink [[grossular]] (right), both [[garnet]]s. The diagnostic features would include dodecahedral crystals, resinous lustre, and hardness around 7.
}}

<!--[[File:Tourmaline.xtal.750pix.jpg|Watermelon [[elbaite]]|left|thumb]]-->
Colour is the most obvious property of a mineral, but it is often non-diagnostic.<ref>{{harvnb|Dyar|Gunter|2008}}, p. 23</ref> It is caused by [[electromagnetic radiation]] interacting with electrons (except in the case of [[incandescence]], which does not apply to minerals).<ref name="DG131144">{{harvnb|Dyar|Gunter|2008}}, pp. 131–44</ref> Two broad classes of elements (idiochromatic and allochromatic) are defined with regards to their contribution to a mineral's colour: Idiochromatic elements are essential to a mineral's composition; their contribution to a mineral's colour is diagnostic.<ref name="B72">{{harvnb|Busbey et al.|2007}}, p. 72</ref><ref name="DG24">{{harvnb|Dyar|Gunter|2008}}, p. 24</ref> Examples of such minerals are [[malachite]] (green) and [[azurite]] (blue). In contrast, allochromatic elements in minerals are present in trace amounts as impurities. An example of such a mineral would be the [[ruby]] and [[sapphire]] varieties of the mineral [[corundum]].<ref name="DG24" />
The colours of pseudochromatic minerals are the result of [[Interference (wave propagation)|interference]] of light waves. Examples include [[labradorite]] and [[bornite]].

In addition to simple body colour, minerals can have various other distinctive optical properties, such as play of colours, [[Asterism (gemmology)|asterism]], [[chatoyancy]], [[iridescence]], tarnish, and [[pleochroism]]. Several of these properties involve variability in colour. Play of colour, such as in [[opal]], results in the sample reflecting different colours as it is turned, while pleochroism describes the change in colour as light passes through a mineral in a different orientation. Iridescence is a variety of the play of colours where light scatters off a coating on the surface of crystal, cleavage planes, or off layers having minor gradations in chemistry.<ref name="DG2426">{{harvnb|Dyar|Gunter|2008}}, pp. 24–26</ref> In contrast, the play of colours in opal is caused by light refracting from ordered microscopic silica spheres within its physical structure.<ref name="B73">{{harvnb|Busbey et al.|2007}}, p. 73</ref> Chatoyancy ("cat's eye") is the wavy banding of colour that is observed as the sample is rotated; asterism, a variety of chatoyancy, gives the appearance of a star on the mineral grain. The latter property is particularly common in gem-quality corundum.<ref name="DG2426" /><ref name="B73"/>

<!--[[File:Streak plate with Pyrite and Rhodochrosite.jpg|thumb|Streak plates with [[pyrite]] (left) and [[rhodochrosite]] (right)|left]]-->
The streak of a mineral refers to the colour of a mineral in powdered form, which may or may not be identical to its body colour.<ref name="DG24" /> The most common way of testing this property is done with a streak plate, which is made out of porcelain and coloured either white or black. The streak of a mineral is independent of trace elements<ref name="B72" /> or any weathering surface.<ref name="DG24" /> A common example of this property is illustrated with [[hematite]], which is coloured black, silver or red in hand sample, but has a cherry-red<ref name="B72" /> to reddish-brown streak;<ref name="DG24" /><ref name=2112.d/> or with [[chalcopyrite]], which is brassy golden in colour and leaves a black streak.<ref name=2112.d/> Streak is more often distinctive for metallic minerals, in contrast to non-metallic minerals whose body colour is created by allochromatic elements.<ref name="B72" /> Streak testing is constrained by the hardness of the mineral, as those harder than 7 powder the ''streak plate'' instead.<ref name="DG24" />

===Cleavage, parting, fracture, and tenacity===
{{main article|Cleavage (crystal)|Fracture (mineralogy)}}
[[File:Biotite-Orthoclase-229808.jpg|left|thumb|Perfect basal cleavage as seen in [[biotite]] (black), and good cleavage seen in the matrix (pink [[orthoclase]]).]]
By definition, minerals have a characteristic atomic arrangement. Weakness in this crystalline structure causes planes of weakness, and the breakage of a mineral along such planes is termed cleavage. The quality of cleavage can be described based on how cleanly and easily the mineral breaks; common descriptors, in order of decreasing quality, are "perfect", "good", "distinct", and "poor". In particularly transparent minerals, or in thin-section, cleavage can be seen as a series of parallel lines marking the planar surfaces when viewed from the side. Cleavage is not a universal property among minerals; for example, quartz, consisting of extensively interconnected silica tetrahedra, does not have a crystallographic weakness which would allow it to cleave. In contrast, micas, which have perfect basal cleavage, consist of sheets of silica tetrahedra which are very weakly held together.<ref name="DG39-40" /><ref name="ChL30-31">{{harvnb|Chesterman|Lowe|2008}}, pp. 29–30</ref>

As cleavage is a function of crystallography, there are a variety of cleavage types. Cleavage occurs typically in either one, two, three, four, or six directions. Basal cleavage in one direction is a distinctive property of the [[mica]]s. Two-directional cleavage is described as prismatic, and occurs in minerals such as the amphiboles and pyroxenes. Minerals such as galena or halite have cubic (or isometric) cleavage in three directions, at 90°; when three directions of cleavage are present, but not at 90°, such as in calcite or [[rhodochrosite]], it is termed rhombohedral cleavage. Octahedral cleavage (four directions) is present in [[fluorite]] and diamond, and [[sphalerite]] has six-directional dodecahedral cleavage.<ref name="DG39-40" /><ref name="ChL30-31"/>

Minerals with many cleavages might not break equally well in all of the directions; for example, calcite has good cleavage in three directions, but gypsum has perfect cleavage in one direction, and poor cleavage in two other directions. Angles between cleavage planes vary between minerals. For example, as the amphiboles are double-chain silicates and the pyroxenes are single-chain silicates, the angle between their cleavage planes is different. The pyroxenes cleave in two directions at approximately 90°, whereas the amphiboles distinctively cleave in two directions separated by approximately 120° and 60°. The cleavage angles can be measured with a contact goniometer, which is similar to a protractor.<ref name="DG39-40" /><ref name="ChL30-31"/>

Parting, sometimes called "false cleavage", is similar in appearance to cleavage but is instead produced by structural defects in the mineral, as opposed to systematic weakness. Parting varies from crystal to crystal of a mineral, whereas all crystals of a given mineral will cleave if the atomic structure allows for that property. In general, parting is caused by some stress applied to a crystal. The sources of the stresses include deformation (e.g. an increase in pressure), exsolution, or twinning. Minerals that often display parting include the pyroxenes, hematite, magnetite, and corundum.<ref name="DG39-40">{{harvnb|Dyar|Gunter|2008}}, pp. 39–40</ref><ref>{{harvnb|Chesterman|Lowe|2008}}, pp. 30–31</ref>

When a mineral is broken in a direction that does not correspond to a plane of cleavage, it is termed to have been fractured. There are several types of uneven fracture. The classic example is conchoidal fracture, like that of quartz; rounded surfaces are created, which are marked by smooth curved lines. This type of fracture occurs only in very homogeneous minerals. Other types of fracture are fibrous, splintery, and hackly. The latter describes a break along a rough, jagged surface; an example of this property is found in [[native copper]].<ref>{{harvnb|Dyar|Gunter|2008}}, pp. 31–33</ref>

Tenacity is related to both cleavage and fracture. Whereas fracture and cleavage describes the surfaces that are created when a mineral is broken, tenacity describes how resistant a mineral is to such breaking. Minerals can be described as brittle, ductile, malleable, sectile, flexible, or elastic.<ref>{{harvnb|Dyar|Gunter|2008}}, pp. 30–31</ref>

===Specific gravity===
[[File:Calcite-Galena-elm56c.jpg|right|thumb|[[Galena]], PbS, is a mineral with a high specific gravity.]]
[[Specific gravity]] numerically describes the [[density]] of a mineral. The dimensions of density are mass divided by volume with units: kg/m<sup>3</sup> or g/cm<sup>3</sup>. Specific gravity is defined as the density of the mineral divided by the density of water at 4&nbsp;°C and thus is a dimensionless quantity, identical in all unit systems.{{sfn|Nesse|2000|p=97}} It can be measured as the quotient of the mass of the sample and difference between the weight of the sample in air and its corresponding weight in water. Among most minerals, this property is not diagnostic. Rock forming minerals&nbsp;– typically silicates or occasionally carbonates&nbsp;– have a specific gravity of 2.5–3.5.<ref name="DG4344">{{harvnb|Dyar|Gunter|2008}}, pp. 43–44</ref>

High specific gravity is a diagnostic property of a mineral. A variation in chemistry (and consequently, mineral class) correlates to a change in specific gravity. Among more common minerals, oxides and sulfides tend to have a higher specific gravity as they include elements with higher atomic mass. A generalization is that minerals with metallic or adamantine lustre tend to have higher specific gravities than those having a non-metallic to dull lustre. For example, [[hematite]], Fe<sub>2</sub>O<sub>3</sub>, has a specific gravity of 5.26<ref>{{cite web|url=https://www.mindat.org/min-1856.html|title=Hematite|publisher=Mindat.org|access-date=3 April 2018|archive-date=11 May 2020|archive-url=https://web.archive.org/web/20200511194050/https://www.mindat.org/min-1856.html|url-status=live}}</ref> while [[galena]], PbS, has a specific gravity of 7.2–7.6,<ref>{{cite web|url=https://www.mindat.org/min-1641.html|title=Galena|publisher=Mindat.org|access-date=3 April 2018|archive-date=11 May 2020|archive-url=https://web.archive.org/web/20200511194055/https://www.mindat.org/min-1641.html|url-status=live}}</ref> which is a result of their high iron and lead content, respectively. A very high specific gravity is characteristic of [[native metal]]s; for example, [[kamacite]], an iron-nickel alloy common in [[iron meteorite]]s has a specific gravity of 7.9,<ref>{{cite web|url=http://webmineral.com/data/Kamacite.shtml#.WsQTQGbn9SM|access-date=3 April 2018|publisher=Webmineral.com|title=Kamacite|archive-date=13 December 2017|archive-url=https://web.archive.org/web/20171213044915/http://webmineral.com/data/Kamacite.shtml#.WsQTQGbn9SM|url-status=live}}</ref> and gold has an observed specific gravity between 15 and 19.3.<ref name="DG4344" /><ref>{{cite web|url=https://www.mindat.org/min-1720.html|title=Gold|publisher=Mindat.org|access-date=3 April 2018|archive-date=27 April 2018|archive-url=https://web.archive.org/web/20180427101610/https://www.mindat.org/min-1720.html|url-status=live}}</ref>

===Other properties===
[[File:Carnotite-201050.jpg|left|thumb|[[Carnotite]] (yellow) is a [[Radioactivity|radioactive]] [[uranium]]-bearing mineral.]]
Other properties can be used to diagnose minerals. These are less general, and apply to specific minerals.

Dropping dilute [[acid]] (often 10% [[hydrochloric acid|HCl]]) onto a mineral aids in distinguishing [[carbonate]]s from other mineral classes. The acid reacts with the carbonate ([CO<sub>3</sub>]<sup>2−</sup>) group, which causes the affected area to [[effervesce]], giving off [[carbon dioxide]] gas. This test can be further expanded to test the mineral in its original crystal form or powdered form. An example of this test is done when distinguishing calcite from [[dolomite (mineral)|dolomite]], especially within the rocks ([[limestone]] and [[dolomite (rock)|dolomite]] respectively). Calcite immediately effervesces in acid, whereas acid must be applied to powdered dolomite (often to a scratched surface in a rock), for it to effervesce.<ref name="DG4445">{{harvnb|Dyar|Gunter|2008}}, pp. 44–45</ref> [[Zeolite]] minerals will not effervesce in acid; instead, they become frosted after 5–10 minutes, and if left in acid for a day, they dissolve or become a [[silica gel]].<ref>{{cite web|url=http://www.minsocam.org/MSA/collectors_corner/id/mineral_id_keyi11.htm|title=Mineral Identification Key: Radioactivity, Magnetism, Acid Reactions|publisher=[[Mineralogical Society of America]]|access-date=2012-08-15|url-status=live|archive-url=https://web.archive.org/web/20120922231836/http://minsocam.org/MSA/collectors_corner/id/mineral_id_keyi11.htm|archive-date=2012-09-22}}</ref>

[[Magnetism]] is a very conspicuous property of a few minerals. Among common minerals, [[magnetite]] exhibits this property strongly, and magnetism is also present, albeit not as strongly, in [[pyrrhotite]] and [[ilmenite]].<ref name="DG4445" /> Some minerals exhibit electrical properties – for example, quartz is [[piezoelectric]] – but electrical properties are rarely used as diagnostic criteria for minerals because of incomplete data and natural variation.<ref name="Helman2016">{{cite journal | title=Symmetry-based electricity in minerals and rocks: A summary of extant data, with examples of centrosymmetric minerals that exhibit pyro- and piezoelectricity | author=Helman, Daniel S. | journal=Periodico di Mineralogia | year=2016 | volume=85 | issue=3 | doi=10.2451/2016PM590}}</ref>

Minerals can also be tested for taste or smell. [[Halite]], NaCl, is table salt; its potassium-bearing counterpart, [[sylvite]], has a pronounced bitter taste. Sulfides have a characteristic smell, especially as samples are fractured, reacting, or powdered.<ref name="DG4445" />

[[Radioactivity]] is a rare property found in minerals containing radioactive elements. The radioactive elements could be a defining constituent, such as [[uranium]] in [[uraninite]], [[autunite]], and [[carnotite]], or present as trace impurities, as in [[zircon]]. The decay of a radioactive element damages the mineral crystal structure rendering it locally [[amorphous]] ([[Metamictisation|metamict state]]); the optical result, termed a ''radioactive halo'' or ''[[pleochroic halo]]'', is observable with various techniques, such as [[thin section|thin-section]] [[petrography]].<ref name="DG4445" />