Editing Mineralogy (section)

==Physical properties==
[[File:Calcit Scalenoeder - Egremont, England.jpg|thumb|[[Calcite]] is a [[carbonate minerals|carbonate mineral]] (CaCO<sub>3</sub>) with a [[rhombohedral]] crystal structure.]]
[[File:Aragonite redbrown crystals.jpg|thumb|[[Aragonite]] is an [[orthorhombic]] polymorph of calcite.]]
 
An initial step in identifying a mineral is to examine its physical properties, many of which can be measured on a hand sample. These can be classified into [[density]] (often given as [[specific gravity]]); measures of mechanical cohesion ([[Mohs scale|hardness]], [[Tenacity (mineralogy)|tenacity]], [[Cleavage (crystal)|cleavage]], [[Fracture (mineralogy)|fracture]], [[Cleavage (crystal)#Parting|parting]]); macroscopic visual properties ([[Luster (mineralogy)|luster]], color, [[Streak (mineralogy)|streak]], [[luminescence]], [[Transparency and translucency|diaphaneity]]); magnetic and electric properties; radioactivity and solubility in [[hydrogen chloride]] ({{chem2|auto=1|HCl}}).<ref name=Ness>{{cite book|last1=Nesse|first1=William D.|title=Introduction to mineralogy|date=2012|publisher=Oxford University Press|location=New York|isbn=978-0199827381|edition=2nd}}</ref>{{rp|97&ndash;113}}<ref name=Klein>{{cite book|last1=Klein|first1=Cornelis |first2=Anthony R. |last2=Philpotts|title=Earth materials : introduction to mineralogy and petrology|date=2013|publisher=Cambridge University Press|location=New York|isbn=9780521145213}}</ref>{{rp|39&ndash;53}}

''Hardness'' is determined by comparison with other minerals. In the [[Mohs scale of mineral hardness|Mohs scale]], a standard set of minerals are numbered in order of increasing hardness from 1 (talc) to 10 (diamond). A harder mineral will scratch a softer, so an unknown mineral can be placed in this scale, by which minerals; it scratches and which scratch it. A few minerals such as [[calcite]] and [[kyanite]] have a hardness that depends significantly on direction.<ref name=Manual/>{{rp|254&ndash;255}} Hardness can also be measured on an absolute scale using a [[sclerometer]]; compared to the absolute scale, the Mohs scale is nonlinear.<ref name=Klein/>{{rp|52}}

''Tenacity'' refers to the way a mineral behaves, when it is broken, crushed, bent or torn. A mineral can be [[brittle]], [[malleable]], [[sectile]], [[ductile]], [[Stiffness|flexible]] or [[elastic deformation|elastic]]. An important influence on tenacity is the type of chemical bond (''e.g.,'' [[ionic bonding|ionic]] or [[metallic bonding|metallic]]).<ref name=Manual/>{{rp|255&ndash;256}} 

Of the other measures of mechanical cohesion, ''cleavage'' is the tendency to break along certain crystallographic planes. It is described by the quality (''e.g.'', perfect or fair) and the orientation of the plane in crystallographic nomenclature. 

''Parting'' is the tendency to break along planes of weakness due to pressure, twinning or [[exsolution]]. Where these two kinds of break do not occur, ''fracture'' is a less orderly form that may be ''[[Conchoidal fracture|conchoidal]]'' (having smooth curves resembling the interior of a shell), ''fibrous'', ''splintery'', ''hackly'' (jagged with sharp edges), or ''uneven''.<ref name="Manual" />{{rp|253&ndash;254}}

If the mineral is well crystallized, it will also have a distinctive [[crystal habit]] (for example, hexagonal, columnar, [[botryoidal]]) that reflects the [[crystal structure]] or internal arrangement of atoms.<ref name=Klein/>{{rp|40&ndash;41}} It is also affected by crystal defects and [[Crystal twinning|twinning]]. Many crystals are [[polymorphism (materials science)|polymorphic]], having more than one possible crystal structure depending on factors such as pressure and temperature.<ref name=Ness/>{{rp|66&ndash;68}}<ref name=Klein/>{{rp|126}}