Alleghanyite

{{Short description|Nesosilicate mineral}}

{{Infobox mineral

| name = Alleghanyite

| category = Nesosilicates
Humite group

| image = Alleghanyite-21573.jpg

| imagesize = 260px

| alt =

| caption = Alleghanyite crystals up to 2 mm in size in a mixed franklinite/calcite/willemite block of 11×6.5×4 cm size. Location: Sterling Mine, Sussex County, New Jersey, US.

| formula = Mn₅(SiO₄)₂(OH)₂

|IMAsymbol=Alh{{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 = 492.87 g/mol

| strunz = 9.AF.45

| dana = 52.3.2b.1

| system = Monoclinic

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

| symmetry = P2₁/a

| unit cell = a = 10.46, b = 4.86
c = 8.3 [Å]; β = 109.133°; Z = 2

| color = Brown, bright pink, grayish pink, white

| habit = Granular; anhedral to subhedral crystals in matrix

| twinning =

| cleavage = None

| fracture = Conchoidal

| tenacity = Brittle

| mohs = 5–6

| luster = Vitreous

| refractive = n_α = 1.756
n_β = 1.78
n_γ = 1.792

| opticalprop = Biaxial (−)

| birefringence = 0.036

| 2V = 72° (meas.), 68° (calc.)

| pleochroism =

| streak =

| gravity = 4 (meas.), 4.11 (calc.)

| density =

| melt =

| fusibility =

| diagnostic =

| solubility =

| diaphaneity = Transparent to translucent

| other = Non-fluorescent

| references = [http://www.mindat.org/min-129.html Alleghanyite]. Mindat[http://webmineral.com/data/Alleghanyite.shtml Alleghanyite]. Webmineral

}}

Alleghanyite is a moderately rare humite mineral with formula Mn₅(SiO₄)₂(OH)₂, belonging to the nesosilicates class. In general its occurrences are related with metamorphic (metamorphosed) manganese deposits. The mineral is named after Alleghany County, North Carolina, US.