Calciohilairite, CaZrSi3O9 · 3H2O, occurs associated with microcline, quartz, albite, fluorite, chlorite, bastnaesite, zircon, and malachite in miarolitic cavities in peralkaline granite of the Eocene Golden Horn batholith, northern Cascades, Washington. The crystals are white to pale blue, trigonal, up to 2 mm long, and show the forms a′ {1120}, ′a {2110}, r {1012}, and −r {0112}. The probable space group is R32; with a = 20.870(4) and c = 16.002(4) Å. The Mohs' hardness is 4, and there is a conchoidal fracture and no cleavage. The density is 2.68(2) g/cm3 (meas.), 2.74 g/cm3 (calc.). The optical properties are uniaxial (−), ϵ = 1.619(1), ω = 1.622(1). The X-ray powder-diffraction pattern, which is very similar to that of hilairite (Na2ZrSi3O9 · 3H2O), shows the following strongest eight lines [d (Å),I,hkl]: 5.99,12,202; 5.23,100,220; 3.14,14,422; 3.02,34,205,600; 2.606,8,440,612,244; 1.817,31,381,725,734; 1.671,17,930,482; 1.668,15,482,384. An average of six electron-microprobe analyses yields the empirical formula

The name is for the Ca content and the relationship to hilairite.

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