cyanotrichite

{{Infobox mineral

| name = Cyanotrichite

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| image = Cyanotrichite-Malachite-249320.jpg

| imagesize = 260px

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| caption = Radiating sprays of cyanotrichite needles on matrix from the old Grand Canyon Mine now within Grand Canyon National Park (size: 3.8 × 3.7 × 1.2 cm)

| category = Sulfate minerals

| formula = Cu₄Al₂[(OH)₁₂|SO₄]·2H₂O

| IMAsymbol=Cya{{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}}

| molweight =

| strunz = 7.DE.10

| dana =

| system = Monoclinic

| class = Prismatic (2/m)
(same H-M symbol)

| symmetry = C2/m

| unit cell = a = 10.16 Å, b = 12.61 Å,
c = 2.9 Å; Z = 1

| color = Sky-blue, azure-blue

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| habit = Acicular crystals and fibrous aggregates; incrustations

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| fracture = Uneven

| tenacity =

| mohs = 1–3

| luster = Silky

| streak = Light blue

| diaphaneity = Transparent to translucent

| gravity = 2.76

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| opticalprop = Biaxial (+)

| refractive = n_α = 1.588 n_β = 1.617 n_γ = 1.655

| birefringence = δ = 0.067

| pleochroism = X = colorless; Y = pale blue; Z = bright blue

| 2V = Measured: 82°

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| references = {{cite web |last1=Anthony |first1=John W. |last2=Bideaux |first2=Richard A. |last3=Bladh |first3=Kenneth W. |last4=Nichols |first4=Monte C. |title=Cyanotrichite |url=http://www.handbookofmineralogy.org/pdfs/cyanotrichite.pdf |website=Handbook of Mineralogy |publisher=Mineral Data Publishing |access-date=3 August 2022 |date=2005}}

| var1 = Polianite | var1text = pseudomorphic after manganite{{mindat|id=6101|title=Polianite|access-date=4 August 2022}}{{mindat|id=1203|title=Cyanotrichite|access-date=4 August 2022}}{{Cite web|last1=Barthelmy|first1=David|year=2014|url=http://www.webmineral.com/data/Cyanotrichite.shtml|access-date=4 August 2022|title = Cyanotrichite Mineral Data|website=Webmineral.com}}[https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Cyanotrichite Mineralienatlas]

}}

Cyanotrichite is a hydrous copper aluminium sulfate mineral with formula Cu₄Al₂[(OH)₁₂|SO₄]·2H₂O, also known as lettsomite. Cyanotrichite forms velvety radial acicular crystal aggregates of extremely fine fibers. It crystallizes in the monoclinic system and forms translucent bright blue acicular crystal clusters or drusey coatings. The Mohs hardness is 2 and the specific gravity ranges from 2.74 to 2.95. Refractive indices are nα = 1.588 nβ = 1.617 nγ = 1.655.