View source for Lepidolite

{{Short description|Phyllosilicate mineral series in the trioctahedral mica group}}
{{Infobox mineral
| name        = Lepidolite
| category    = [[Phyllosilicate]] [[minerals]], trioctahedral [[mica]] [[Mineral group|group]]
| boxwidth    =
| boxbgcolor  = #cccccc
| image       = Boromuscovite-Lepidolite-ch38a.jpg
| imagesize   = 260px
| caption     = 
| formula     = {{chem2|K(Li,Al)3(Al,Si)4O10(F,OH)2}}
| IMAsymbol   = Lpd<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>
| molweight   =
| strunz      = 9.EC.20
| system      = [[Monoclinic]]
| class       = Prismatic (2/m) <br /><small>(same [[H-M symbol]])</small>
| symmetry    = ''C''2/m, ''Cm''
| unit cell   = a = 5.209(2)&nbsp;[[angstrom|Å]], b = 9.011(5)&nbsp;Å,  <br />c = 10.149(5)&nbsp;Å; <br />β = 100:77(4)°; Z&nbsp;=&nbsp;2
| color       = Pink, light purple, purple, rose-red, violet-gray, yellowish, white, colorless other colors possible but are rare.
| habit       = Tabular to prismatic pseudohexagonal crystals, scaly aggregates and massive
| twinning    = Rare, composition plane {001}
| cleavage    = {001} perfect
| fracture    = Uneven
| mohs        = 2.5–3
| luster      = Vitreous to pearly
| polish      =
| refractive  = n<sub>α</sub>=1.525–1.548, n<sub>β</sub>=1.551–1.58, n<sub>γ</sub>=1.554–1.586
| opticalprop = Biaxial (−)
| birefringence = 0.0290–0.0380
| dispersion  =
| 2V          =  0° – 58° measured
| pleochroism = X = almost colorless; Y = Z = pink, pale violet
| fluorescence=
| absorption  =
| streak      = White
| gravity     = 2.8–2.9
| density     =
| melt        =
| fusibility  =
| diagnostic  =
| solubility  =
| diaphaneity = Transparent to translucent
| other       =
| references  = <ref name=Handbook>{{cite web |last1=Anthony |first1=John W. |last2=Bideaux |first2=Richard A. |last3=Bladh |first3=Kenneth W. |last4=Nichols |first4=Monte C. |title=Lepidolite |url=http://www.handbookofmineralogy.org/pdfs/lepidolite.pdf |website=Handbook of Mineralogy |publisher=Mineral Data Publishing |access-date=14 March 2022 |date=2005}}</ref><ref name=Webmin>{{Cite web |url=http://www.webmineral.com/data/Lepidolite.shtml |access-date=19 March 2022 |title = Lepidolite Mineral Data |website=Webmineral.com |first1=David |last1=Barthelmy |year=2014}}</ref>
}}

'''Lepidolite''' is the common name for a [[Lilac (color)|lilac]]-gray or rose-colored series of minerals in the [[mica]] group. The mineralogical name for this series is the '''polylithionite-trilithionite series'''.<ref name="mindat" /> Lepidolite has a chemical formula of {{chem2|K(Li,Al)3(Al,Si)4O10(F,OH)2}}.<ref name=Handbook/><ref name=Webmin/> It is the most abundant [[lithium]]-bearing mineral<ref name="DHZ1966">{{cite book | title=An Introduction to the Rock Forming Minerals | last1=Deer | first1=W.A. | last2=Howie | first2=R.A. | last3=Zussman | first3=J. | publisher=Longman | year=1966 | location=London | pages=218 | isbn=0-582-44210-9}}</ref> and is a secondary source of this metal. It is also the major source of the [[alkali metal]] [[rubidium]], which substitutes (as in all minerals) for [[potassium]].

Lepidolite is found with other lithium-bearing minerals, such as [[spodumene]], in [[pegmatite]] bodies. It has also been found in high-temperature quartz veins, [[greisen]]s and granite.

==Description==
Lepidolite is a [[silicate minerals|phyllosilicate]] mineral<ref>Hurlbut, Cornelius S.; Klein, Cornelis (1985), ''Manual of Mineralogy,'' Wiley, (20th ed.) {{ISBN|0-471-80580-7}}</ref> and a member of the polylithionite-trilithionite series.<ref name="mindat">{{cite web |title=Lepidolite |url=https://www.mindat.org/min-2380.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=24 February 2025}}</ref> Lepidolite is part of a three-part series consisting of polylithionite, lepidolite, and trilithionite. All three minerals share similar properties and are caused because of varying ratios of lithium and aluminum in their chemical formulas. The Li:Al ratio varies from 2:1 in polylithionite up to 1.5:1.5 in trilithionite.<ref>{{mindat|id=28887|title=Polylithionite-Trilithionite Series}}</ref><ref name=RiederEtal1999>{{cite journal |last1=Rieder |first1=M. |last2=Cavazzini |first2=G. |last3=D’yakonov |first3=Yu. S. |last4=Frank-Kamenetskii |first4=V. A. |last5=Gottardi |first5=G. |last6=Guggenheim |first6=S. |last7=Koval’ |first7=P. V. |last8=Müller |first8=G. |last9=Neiva |first9=A. M. R. |last10=Radoslovich |first10=E. W. |last11=Robert |first11=J.-L. |last12=Sassi |first12=F. P. |last13=Takeda |first13=H. |last14=Weiss |first14=Z. |last15=Wones |first15=D. R. |title=Nomenclature of the micas |journal=Mineralogical Magazine |date=April 1999 |volume=63 |issue=2 |pages=267–279 |doi=10.1180/minmag.1999.063.2.13|bibcode=1999MinM...63..267R |s2cid=62814673 }}</ref>

Lepidolite is found naturally in a variety of colors, mainly pink, purple, and red, but also gray and, rarely, yellow and colorless. Because lepidolite is a lithium-bearing mica, it is often wrongly assumed that lithium is what causes the pink hues that are so characteristic of this mineral. Instead, it is trace amounts of manganese that cause the pink, purple, and red colors.<ref>{{Cite web|url=https://geology.com/minerals/lepidolite.shtml|title = Lepidolite: A pink to purple mica, a source of lithium, an ornamental stone, a gem material |first1=Hobart M. |last1=King |publisher=geology.com |access-date=19 March 2022}}</ref><ref>{{cite journal |last1=London |first1=David |title=Reading Pegmatites: Part 3—What Lithium Minerals Say |journal=Rocks & Minerals |date=4 March 2017 |volume=92 |issue=2 |pages=144–157 |doi=10.1080/00357529.2017.1252636|bibcode=2017RoMin..92..144L |s2cid=132383641 }}</ref>

===Structure and composition===
Lepidolite belongs to the group of trioctahedral micas,<ref name=RiederEtal1999/> with a structure resembling [[biotite]]. This structure is sometimes described as ''TOT-c''. The crystal consists of stacked ''TOT'' layers weakly bound together by potassium ions (''c''). Each ''TOT'' layer consists of two outer ''T'' (tetrahedral) sheets in which silicon or aluminium ions each bind with four oxygen atoms, which in turn bind to other aluminium and silicon to form the sheet structure. The inner ''O'' (octahedral) sheet contains iron or magnesium ions each bonded to six oxygen, fluoride, or hydroxide ions. In biotite, silicon occupies three out of every four tetrahedal sites in the crystal and aluminium occupies the remaining tetrahedral sites, while magnesium or iron fill all the available octahedral sites.<ref name=KleinHurlbut1993>{{cite book |last1=Klein |first1=Cornelis |last2=Hurlbut |first2=Cornelius S. Jr. |title=Manual of mineralogy : (after James D. Dana) |date=1993 |publisher=Wiley |location=New York |isbn=047157452X |edition=21st |pages=498–507}}</ref>

Lepidolite shares this structure, but aluminium and lithium substitute for magnesium and iron in the octahedral sites. If nearly equal quantities of aluminium and lithium occupy the octahedral sites, the resulting mineral is trilithionite, {{chem2|KLi1.5Al1.5(AlSi3)O10(F,OH)2}} If lithium occupies two out of three octahedral sites and aluminium the remaining octahedra site, then charge balance can be preserved only if silicon occupies all the tetrahedral sites. The result is polylithionite, {{chem2|KLi2AlSi4O10(F,OH)2}}. Lepidolite has a composition intermediate between these end members.<ref name=RiederEtal1999/>

Fluoride ions can substitute for some of the hydroxide in the structure, while [[sodium]], [[rubidium]], or [[caesium]] may substitute in small quantities for potassium.{{sfn|Klein|Hurlbut|1993|p=519}}

==Occurrences==
Lepidolite is associated with other lithium-bearing minerals like [[spodumene]] in [[pegmatite]] bodies.  It is the major source of the [[alkali metal]] [[rubidium]].<ref>{{Cite journal |title =Trace element chemistry of lithium-rich micas from rare-element granitic pegmatites |volume = 55
| issue = 13 |date = 1995 |doi = 10.1007/BF01162588 |pages = 203–215 |journal = Mineralogy and Petrology |first = M. A. |last = Wise |bibcode = 1995MinPe..55..203W |s2cid = 140585007
}}</ref> In 1861, [[Robert Bunsen]] and [[Gustav Kirchhoff]] extracted {{convert|150|kg|abbr=on}} of lepidolite to yield a few grams of rubidium salts for analysis, and therefore discovered the new element rubidium.<ref>{{cite journal
 | title = Chemische Analyse durch Spectralbeobachtungen
 | pages = 337–381
 | author = G. Kirchhoff, R. Bunsen
 | doi = 10.1002/andp.18611890702
 | journal = [[Annalen der Physik und Chemie]]
 | volume = 189
 | issue = 7
 | year = 1861
 | bibcode=1861AnP...189..337K| url = http://archiv.ub.uni-heidelberg.de/volltextserver/15657/1/spektral.pdf
 }}</ref><ref name="Weeks">{{Cite journal |title = The discovery of the elements. XIII. Some spectroscopic discoveries |pages = 1413–1434 |last = Weeks |first = Mary Elvira |author-link=Mary Elvira Weeks|doi=10.1021/ed009p1413 |journal = [[Journal of Chemical Education]] |volume =9 |issue =8 |date = 1932 |bibcode=1932JChEd...9.1413W}}</ref>

It occurs in [[granite]] [[pegmatite]]s, in some high-temperature quartz veins, [[greisen]]s and granites. Associated minerals include [[quartz]], [[feldspar]], [[spodumene]], [[amblygonite]], [[tourmaline]], [[columbite]], [[cassiterite]], [[topaz]] and [[beryl]].<ref name=Handbook/>

Notable occurrences include [[Brazil]]; [[Ural Mountains]], Russia; [[California]] and the [[Black Hills]], United States; [[Tanco Mine]], [[Bernic Lake]], [[Manitoba]], Canada; and [[Madagascar]].<ref name=Handbook/>

<gallery  widths="200px" heights="200px">
File:Lepidolite-140533.jpg|Yellow lepidolite from [[Itinga]],  [[Minas Gerais]], Brazil. Size: 6.1 x 4.9 x 3.1&nbsp;cm
File:Lepidolite-208658.jpg|Lavender lepidolite "books" from Himalaya Mine, Mesa Grande District, [[San Diego County, California]], US. Size: 4.8 x 3.9 x 3.5&nbsp;cm
File:Lepidolite-76774.jpg|Lepidolite, [[Virgem da Lapa]],  [[Minas Gerais]], Brazil (size 2.4 x 2.1 x 0.7&nbsp;cm)
File:Radiating lepidolite White Elephant Mine SD.jpg|Radiating lepidolite at the White Elephant pegmatite, Black Hills, South Dakota
</gallery>

==References==
{{Commons category}}
{{Reflist}}

{{Phyllosilicates}}
{{Lithium compounds}}
{{Authority control}}

[[Category:Lithium minerals]]
[[Category:Potassium minerals]]
[[Category:Aluminium minerals]]
[[Category:Monoclinic minerals]]
[[Category:Minerals in space group 8]]
[[Category:Minerals in space group 12]]
[[Category:Luminescent minerals]]
[[Category:Gemstones]]
[[Category:Rubidium compounds]]
[[Category:Trioctahedral mica group]]