greifensteinite

{{Short description|Beryllium phosphate mineral}}

{{Infobox mineral

| name = Greifensteinite

| image = Greifensteinite-MA1277056257.jpg

| imagesize = 260px

| alt =

| caption = Greifensteinite (picture size: 3 mm)

| category = Phosphate mineral
Roscherite group

| formula = Ca₂Fe²⁺₅Be₄(PO₄)₆(OH)₄·6H₂O

| IMAsymbol = Gfs{{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}}

| strunz = 8.DA.10

| dana = 42.7.7.4

| system = Monoclinic

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

| symmetry = C2/c

| unit cell = a = 15.903, b = 11.885
c = 6.677 [Å]; β = 94.68°; Z = 2

| color = Yellow green, olive green, light brown

| habit = Prismatic

| twinning =

| cleavage = Good on {100} (or parting on {100})

| fracture = Uneven

| tenacity = brittle

| mohs = 4.5

| luster = Vitreous

| streak = White, greenish

| diaphaneity = Transparent to translucent

| gravity = 2.93

| density =

| polish =

| opticalprop = Biaxial (-)

| refractive = n_α: 1.624
n_β: 1.634
n_γ: 1.638

| birefringence = 0.014

| pleochroism =

| 2V = 80°

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| references =[http://www.webmineral.com/data/Greifensteinite.shtml#.UueuR9LnbRY Greifensteinite data on Webmineral][http://www.mindat.org/min-11356.html Mindat.org][http://www.mineralienatlas.de/lexikon/index.php/MineralData?lang=en&language=english&mineral=Greifensteinite Mineralienatlas]

}}

Greifensteinite is beryllium phosphate mineral with formula: Ca₂Fe²⁺₅Be₄(PO₄)₆(OH)₄·6H₂O. It is the Fe²⁺ dominant member of the roscherite group.[http://www.mindat.org/min-39378.html Roscherite group on Mindat.org] It crystallizes in the monoclinic crystal system and typically forms prismatic dark olive green crystals.

It was first described in Germany at Greifenstein Rocks, Ehrenfriedersdorf, and was named for the location. At the type locality, it occurs within a lithium-rich pegmatite in miarolitic cavities. It was approved by the International Mineralogical Association in 2002.