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Hogarthite, (Na,K) (sub 2) CaTi (sub 2) Si (sub 10) O (sub 26) .8H (sub 2) O, a new mineral of the lemoynite group, was discovered in vugs within metasomatically altered marble xenoliths in the Poudrette quarry, Mont Saint-Hilaire, La-Vallee-du-Richelieu RCM, Monteregie, Quebec, Canada. Crystals are bladed to blocky, average 0.05 X 0.15 X 2 mm in size, and range in color from tan to white to colorless. The mineral develops in dense, radiating crystal aggregates up to 0.5 X 3 mm in size, and is associated with calcite (several generations), quartz, haineaultite, labuntsovite-Mn, lemoynite, chabazite, and gmelinite-Na. Crystals are elongate along [100], flattened on {010} and are bounded by the forms pinacoid {010} (dominant), pinacoid {100} (minor), and pinacoid {001} (minor). The mineral has a white streak, is non-fluorescent under short-, medium-, and long-wave ultraviolet radiation, is translucent, and has a satiny to silky to subvitreous luster. It has a brittle fracture, a perfect {010} cleavage, a hackly to splintery fracture, an estimated hardness of 4, and D (sub calc) = 2.40(1) g/cm (super 3) . Hogarthite is biaxial (+) with alpha 1.567(1), beta 1.591(1), and gamma 1.618(1) with 2V (sub meas) = 87(1) degrees and 2V (sub calc) = 88(1) degrees . The optical orientation is X = b, Y degrees c = 15 degrees (measured in the obtuse angle beta ), Z = a. A total of 21 analyses, obtained from seven crystals, gave an average (range) of (wt.%): Na (sub 2) O 2.37 (1.69-2.92), K (sub 2) O 2.88 (2.61-3.17), CaO 6.00 (5.40-6.31), TiO (sub 2) 14.44 (13.70-15.83), ZrO (sub 2) 1.11 (0.48-1.73), Nb (sub 2) O (sub 5) 0.78 (0.42-1.24), SiO (sub 2) 59.27 (57.32-60.64), H (sub 2) O 14.10 (calc.), total 100.95. The empirical formula (based on 34 anions) is (Na (sub 0.78) K (sub 0.62) (sub 0.51) Ca (sub 0.09) ) (sub Sigma 2.00) Ca(Ti (sub 1.85) Zr (sub 0.09) Nb (sub 0.06) ) (sub Sigma 2.00) Si (sub 10.09) O (sub 26) .8H (sub 2) O, and the simplified formula is (Na,K) (sub 2) CaTi (sub 2) Si (sub 10) O (sub 26) .8H (sub 2) O. The presence of (OH) and H (sub 2) O were confirmed via refinement of the crystal-structure and data from combined FTIR and Raman spectroscopies. The mineral crystallizes in space group C2/m with a 10.1839(5), b 15.8244(6), c 9.1327(7) Aa, beta 104.463(2)?, V 1425.1(1) Aa (super 3) , and Z = 2. The strongest six lines on the X-ray powder diffraction pattern [d in Aa (I) (hkl)] are: 8.835 (85) (001), 7.913 (100) (020), 6.849 (70) (111), 4.336 (45) (131, [112), 3.514 (80) (221), 3.426 (55) (222, 132). The crystal structure, refined to R = 0.049 for 1335 reflections (F (sub o) > 4sigma F (sub o) ), consists of a silicate component, composed of interconnected, non-planar 10-membered rings, arranged into thick slabs and stacked along [001]. These are interleaved with layers of independent TiO (sub 6) octahedra, producing a framework of composition [TiSi (sub 5) O (sub 13) ] (super 2-) . Numerous channels within the framework, notably the continuous ones developed by 10-membered silicate rings, are occupied by Na, Ca, and H (sub 2) O groups. Hogarthite is considered to be a product of late-stage alkaline fluid enriched in SiO (sub 2) and TiO (sub 2) , and forming under conditions of low P at T < 200 degrees C, possibly through crystallization of a gel.

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GeoRef, Copyright 2018, American Geological Institute.<br/>2015-094139<br/>haineaultite<br/>hogarthite<br/>lemoynite<br/>Poudrette Quarry