cuspidine

{{infobox mineral

| name = Cuspidine

| image = File:Cuspidine.jpg

| alt =

| caption = Yellowish cuspidine crystals from the type locality at Mount Vesuvius

| category = Sorosilicate

| formula = Ca₄(Si₂O₇)(F,OH)₂

| IMAsymbol=Csp{{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 = 9.BE.17

| dana =

| system = Monoclinic

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

| symmetry = P2₁/c

| unit cell = a = 10.93 Å, b = 10.57 Å,
c = 7.57 Å; β = 110.11°; Z=4

| color = Colorless, tan, light brown, pale red

| habit = Minute spearhead-shaped crystals, acicular, granular

| twinning = Simple, lamellar, polysynthetic on {100}

| cleavage = Good on {001} imperfect on {110}

| fracture = Uneven

| tenacity = Brittle

| mohs = 5–6

| luster = Vitreous

| streak =

| diaphaneity = Transparent to translucent

| gravity = 2.85–2.96

| density =

| polish =

| opticalprop = Biaxial (+)

| refractive = n_α = 1.586 – 1.594 n_β = 1.589 – 1.596 n_γ = 1.598 – 1.606

| birefringence = δ = 0.012

| pleochroism =

| 2V = Measured: 59° to 71°

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| references = [http://www.mindat.org/min-1198.html Cuspidine on Mindat.org][http://www.webmineral.com/data/Cuspidine.shtml#.UuQ9vdLnbRY Cuspidine data on Webmineral ][http://rruff.info/doclib/hom/cuspidine.pdf Cuspidine in the Handbook of Mineralogy]

}}

Cuspidine is a fluorine bearing calcium silicate mineral (sorosilicate) with formula: Ca₄(Si₂O₇)(F,OH)₂. Cuspidine crystallizes in the monoclinic crystal system and occurs as acicular to spear shaped pale red to light brown crystals. It is a member of the wöhlerite group.

Cuspidine was first described in 1876 for an occurrence in Monte Somma, Italy. The name is from the Greek cuspis for spear from its characteristic crystal form. Cuspidine occurs as crystals in tuff from Monte Somma. In the Franklin, New Jersey mine area it occurs in contact metamorphosed limestone. In Dupezeh Mountain, Iraq, it occurs in melilite bearing skarn. Associated minerals include augite, hornblende, diopside, grossular, biotite, phlogopite, monticellite, wollastonite, calcite, spinel, magnetite and perovskite.