Lustre (mineralogy) 60652 226004994 2008-07-16T12:11:00Z Hyperdeath 1254298 /* Greasy lustre */ '''Lustre''' (or '''luster''') is a description of the way light interacts with the surface of a [[crystal]], [[rock (geology)|rock]], or [[mineral]]. For example, a [[diamond]] is said to have an ''[[adamantine]]'' lustre and [[pyrite]] is said to have a ''metallic'' lustre. The term is also used to describe other items with a particular sheen (for example, [[cloth|fabric]], especially [[silk]] and [[satin]], or [[metal]]s). The word ''lustre'' traces its origins back to the [[Latin]] word ''lux'', meaning "light", and generally implies radiance, gloss, or brilliance. ==Terminology== A broad range of terms are used to describe the lustre of minerals. It should be noted that lustre varies over a wide continuum, and so there are no rigid boundaries between the different terms. (For this reason, different sources can often describe the same mineral differently. This ambiguity is further complicated by the fact that lustre can vary widely within a particular mineral species.) The terms are frequently combined to describe intermediate types of lustre (for example, a "vitreous greasy" lustre). ====Adamantine lustre==== [[Image:Brillanten.jpg|thumb|left|180px|Cut [[diamond|diamonds]]]] '''[[Adamantine]]''' minerals possess a superlative lustre, which is most notably seen in [[diamond]].<ref name="GRG">[[Gemological Institute of America]], ''GIA Gem Reference Guide'' 1995, ISBN 0-87311-019-6</ref> Such minerals are transparent or translucent, and have a high [[refractive index]] (of 1.9 or more).<ref name="duda_rejl">{{cite book| title = Minerals of the World| author = Duda, Rudolf & Rejl, Lubos| publisher = Arch Cape Press| year = 1990| isbn = 0-517-68030-0}}</ref> Minerals with a true adamantine lustre are uncommon, with other examples being [[cerussite]] and [[zircon]].<ref name="duda_rejl" /> Minerals with a lesser (but still relatively high) degree of lustre are referred to as '''subadamantine''', with an example being [[garnet]].<ref name="GRG" /> <br clear="all" /> ====Dull lustre==== [[Image:KaolinUSGOV.jpg|thumb|left|180px|[[Kaolinite]]]] '''Dull''' (or '''earthy''') minerals exhibit little to no lustre, due to coarse granulations which scatter light in all directions, approximating a [[Lambertian reflectance|Lambertian reflector]]. An example is [[kaolinite]].<ref name="webmineral_kaolinite">{{cite web| url = http://www.webmineral.com/data/Kaolinite.shtml| title = Webmineral: Kaolinite Mineral Data| accessdate=2008-06-21}}</ref> A distinction is sometimes drawn between dull minerals and earthy minerals,<ref>{{cite book| title = Rocks, Crystals & Minerals| last=Hankin| first=Rosie| publisher = Quintet Publishing| isbn = 1-86155-480-X| year = 1998 }}</ref> with the latter being coarser, and having even less lustre. <br clear="all" /> ====Greasy lustre==== [[Image:Moos-Opal1.jpg|thumb|left|180px|Moss [[opal]]]] '''Greasy''' minerals resemble fat or grease. A greasy lustre often occurs in minerals containing a great abundance of microscopic inclusions, with examples including [[opal]] and [[cordierite]].<ref name="duda_rejl" /> Many minerals with a greasy lustre also ''feel'' greasy.<ref name="GO_340">{{cite web| url = http://www.emporia.edu/earthsci/amber/go340/visual.htm| title = Emporia State University: GO 340 Gemstones & Gemology: Visual Properties| accessdate=2008-06-19}}</ref> <br clear="all" /> ====Metallic lustre==== [[Image:Pyrite foolsgold.jpg|thumb|left|180px|[[Pyrite]]]] '''Metallic''' (or '''splendent''') minerals have the lustre of polished metal (and with ideal surfaces will act like a [[mirror]]). Examples include [[galena]],<ref name="webmineral_galena">{{cite web| url = http://webmineral.com/data/Galena.shtml| title = Webmineral: Galena Mineral Data| accessdate=2008-07-05}}</ref> [[pyrite]]<ref name="webmineral_pyrite">{{cite web| url = http://webmineral.com/data/Pyrite.shtml| title = Webmineral: Pyrite Mineral Data| accessdate=2008-07-05}}</ref> and [[magnetite]].<ref name="webmineral_magnetite">{{cite web| url = http://webmineral.com/data/Magnetite.shtml| title = Webmineral: Magnetite Mineral Data| accessdate=2008-07-05}}</ref> <br clear="all" /> ====Pearly lustre==== [[Image:Mineral Mica GDFL006.JPG|thumb|left|180px|[[Muscovite]]]] '''Pearly''' minerals consist of thin transparent co-planar sheets. Light reflecting from these layers give them a lustre reminiscent of [[pearl|pearls]].<ref name="rockcollector" /> Such minerals possess perfect [[Cleavage (crystal)|cleavage]], with examples including [[muscovite]] and [[stilbite]].<ref name="duda_rejl" /> <br clear="all" /> ====Resinous lustre==== [[Image:Amber hg.jpg|thumb|left|180px|[[Amber]]]] '''Resinous''' minerals have the appearance of [[resin]], [[chewing gum]] or (smooth surfaced) plastic. A principal example is [[amber]], which is a form of fossilized resin.<ref name="webmineral_amber">{{cite web| url = http://webmineral.com/data/Amber.shtml| title = Webmineral: Amber Mineral Data| accessdate=2008-06-21}}</ref> <br clear="all" /> ====Silky lustre==== [[Image:Selenite Gips Marienglas.jpg|thumb|left|180px|[[Satin spar]] variety of [[gypsum]]]] '''Silky''' minerals have a parellel arrangement of extremely fine fibres,<ref name="duda_rejl" /> giving them a lustre reminiscent of [[silk]]. Examples include [[asbestos]], [[ulexite]] and the [[satin spar]] variety of [[gypsum]]. A '''fibrous''' lustre is similar, but has a coarser texture. <br clear="all" /> ====Submetallic lustre==== [[Image:Sphalerite4.jpg|thumb|left|180px|[[Sphalerite]]]] '''Submetallic''' minerals have similar lustre to metal, but are duller and less reflective. A submetallic lustre often occurs in near-opaque minerals with very high refractive indices,<ref name="duda_rejl" /> such as [[sphalerite]], [[cinnabar]] and [[cuprite]]. <br clear="all" /> ====Vitreous lustre==== [[Image:USDA_Mineral_Quartz_Crystal_93c3951.jpg|thumb|left|180px|[[Quartz]]]] '''Vitreous''' minerals have the lustre of [[glass]]. This type of lustre is one of the most commonly seen,<ref name="rockcollector">{{cite web| url = http://www.rockcollector.co.uk/opticalprop.htm| title = Optical properties of Rocks and Minerals| accessdate=2008-06-01}}</ref> and occurs in transparent or translucent minerals with relatively low refractive indices.<ref name="duda_rejl" /> Common examples include [[calcite]], [[quartz]] and [[fluorite]]. <br clear="all" /> ====Waxy lustre==== [[Image:Jadestein.jpg|thumb|left|180px|[[Jade]]]] '''Waxy''' minerals have a lustre resembling [[wax]]. Examples include [[jade]]<ref name="emporia_jade">{{cite web| url =http://www.emporia.edu/earthsci/amber/go340/jade.htm| title = Emporia State University: GO 340 Gemstones & Gemology: Jade| accessdate=2008-07-14}}</ref> and [[chalcedony]].<ref name="rock_and_gem">{{cite book |last=Bonewitz |first=Ronald Louis |title=Rock and Gem |year=2005 |id=ISBN 0-7513-4400-1 |pages=pp.&nbsp;152 &ndash; 153 |publisher=[[Dorling Kindersley]]}}</ref> <br clear="all" /> ==Optical phenomena== ====Asterism==== [[Image:Star-Saphire.jpg|thumb|left|180px|[[Sapphire]] cabochon]] '''[[Asterism (gemmology)|Asterism]]''' is the display of a star-shaped luminous area. It is seen in some [[Sapphire|sapphires]] and [[ruby|rubies]], where it is caused by impurities of [[rutile]].<ref name="rock_and_gem" /><ref name="BuildingBlocks451-3">{{cite book |last=Emsley |first=John |title=Nature's Building Blocks: An A-Z Guide to the Elements |year=2001 |id=ISBN 0-19-850341-5 |pages=pp.&nbsp;451 &ndash; 53 |publisher=[[Oxford University Press]]}}</ref> It can also occur in [[garnet]], [[diopside]] and [[spinel]]. <br clear="all" /> ====Aventurescence==== [[Image:Aventurine.jpg|thumb|left|180px|[[Aventurine]]]] '''[[Aventurescence]]''' (or '''aventurization''') is a reflectance effect like that of [[glitter]]. It arises from minute, preferentially oriented mineral platelets within the material. These platelets are so numerous that they also influence the material's body colour. In [[aventurine|aventurine quartz]] chrome-bearing [[fuchsite]] makes for a green stone, and various [[iron oxide|iron oxides]] make for a red stone.<ref name="rock_and_gem" /> <br clear="all" /> ====Chatoyancy==== [[Image:Tigers-Eye.jpg|thumb|left|180px|[[Tiger's eye]]]] '''[[Chatoyancy|Chatoyant]]''' minerals display luminous bands, which appear to move as the specimen is rotated. Such minerals are composed of parallel fibers (or contain fibrous voids or inclusions), which reflect light into a direction perpendicular to their orientation, thus forming narrow bands of light. The most famous examples are [[tiger's eye]] and [[Chrysoberyl#Cymophane|cymophane]], but the effect may also occur in other minerals such as [[aquamarine]], [[Moonstone_(gemstone)|moonstone]] and [[tourmaline]]. <br clear="all" /> ====Schiller==== [[Image:Labradoryt, Madagaskar.JPG|thumb|left|180px|[[Labradorite]]]] '''Schiller''' is a term used to describe the colourful iridescence that occurs when light is reflected between layers. It is seen in [[Moonstone (gemstone)|moonstone]] and [[labradorite]]. <br clear="all" /> == See also == * [[Adamantine]] * [[Asterism (gemmology)]] * [[Aventurescence]] * [[Chatoyancy]] * [[Hornblende]] ==References== <references /> [[Category:Mineralogy]] [[cs:Lesk]] [[de:Glanz]] [[es:Lustre]] [[et:Läige]] [[fr:Éclat]] [[it:Lucentezza dei minerali]] [[ja:光沢]] [[lv:Spīdums (mineraloģija)]] [[nl:Glans]] [[pt:Lustre]] [[ru:Блеск (геология)]] [[fi:Kiilto (mineralogia)]] {{Template: Mineral identification}}