sellaite

{{infobox mineral

| name = Sellaite

| boxwidth =

| boxbgcolor =

| image = Sellaite-39033.jpg

| imagesize = 150px

| alt =

| caption = Sellaite crystal from Serra das Éguas, Brazil (size: 4.2 × 2.4 × 2 cm)

| category = Halide mineral

| formula = MgF₂

| IMAsymbol = Sel{{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 = 3.AB.15

| dana =

| system = Tetragonal

| class = Ditetragonal dipyramidal (4/mmm)
H-M symbol: (4/m 2/m 2/m)

| symmetry = P4₂/mnm

| unit cell = a = 4.6213(2) Å
c = 3.0519(1) Å
Z = 2

| color = Colorless to white

| colour =

| habit = Prismatic crystals; fibrous, radial, spherulitic

| twinning = On {011}

| cleavage = Perfect on {010} and {110}

| fracture = Conchoidal

| tenacity = Brittle

| mohs = 5–5.5

| luster = Vitreous

| streak =

| diaphaneity = Transparent

| gravity = 3.15

| density =

| polish =

| opticalprop = Uniaxial (+)

| refractive = n_ω = 1.378
n_ε = 1.390

| birefringence = δ = 0.012

| pleochroism =

| 2V =

| dispersion =

| extinction =

| length fast/slow =

| fluorescence =

| absorption =

| melt =

| fusibility =

| diagnostic =

| solubility =

| impurities =

| alteration =

| references = [http://rruff.geo.arizona.edu/doclib/hom/sellaite.pdf Mineral Data Publishing: Handbook of Mineralogy][http://www.mindat.org/min-3614.html Mindat with location data].[http://webmineral.com/data/Sellaite.shtml Webmineral data].

}}

Sellaite is a magnesium fluoride mineral with the formula MgF₂. It crystallizes in the tetragonal crystal system, typically as clear to white vitreous prisms. It may be fibrous and occur as radiating aggregates. It has a Mohs hardness of 5 to 6 and a specific gravity of 2.97 to 3.15. Refractive index values are n_ω = 1.378 and n_ε = 1.390.