Bigcreekite, ideally BaSi2O5·4H2O, is a newly identified mineral species that occurs along
very thin transverse fractures in fairly well-laminated
quartz-rich sanbornite portions of the rock.
Bigcreekite is biaxial negative, with indices of refraction
h1=1.537(2), h2= 1.538(2), h3= 1.541(2); X = b,
Y =a, Z = c and 2V[submeas]= 59.2°
, 2V[sub calc]= 60.1°.
The crystal structure of bigcreekite was solved as space
group Pnma, with cell parameters a = 5.038? ,
b = 9.024 ? , c = 18.321 ? , and Z = 4.
Bigcreekite is
a hydrous chain silicate containing four-membered
rings which form chains of silica tetrahedra, parallel to
[100] and staggered in the [001] direction. Water molecules
fill the large spaces between the rows of silicon
tetrahedra.
