MARSTURITE Chapter17. Inosilicates

MARSTURITE

Triclinic, P1 or P1, a = 7.70, b = 12.03, c = 6.78 Å,
a = 85.26 b = 94.10, g = 111.04^o, Z = 2




	Figure 17-15. Bladed, triclinic marsturite crystals from Franklin. Field of view is 5 mm in maximum dimension.

Marsturite was first described by Peacor et al. (1978) from Franklin. Another habit, previously referred to as bustamite by Larsen and Shannon (1922b), was found to be marsturite epitactic on rhodonite by Dunn and Leavens (1986). Marsturite has not been reported from Sterling Hill.

Description

Marsturite crystals are bladed in habit and elongate on [010] (Figures 17-15, 17-16, and 17-18). Forms present are {001} (dominant pinacoid), {100} (the subordinate pinacoid), and an impefectly defined {010} pinacoid. Crystal faces are frosty, giving a subtranslucent appearance. Marsturite is colorless to light pink, with vitreous luster, imperfect cleavages on {100} and {001}, and a density of 3.46 g/cm³. Optically, marsturite is biaxial, positive, 2V = 60^o, with a = 1.686, b = 1.691, and g = 1.708; dispersion is very weak, r > v. There is no discernible fluorescence in ultraviolet.




	Figure 17-16. Bladed marsturite crystals from Franklin. Field of view is 0.5 mm in maximum dimension.		Figure 17-17. Light-colored marsturite rims on rhodonite crystals (gray inside marsturite) from Franklin. Field of view is approximately 2.5 cm in maximum dimension. Smithsonian Institution, #C2485-1. Photo by Vic Krantz.

Composition

Marsturite is a sodium calcium manganese silicate of the pyroxenoid group and is related to nambulite. Several analyses are given in Table 10 and conform closely to the theoretical composition. There is little substitution of Fe and Mg for Mn.




	Figure 17-18. Bladed marsturite crystals from Franklin. Field of view is 0.4 mm in maximum dimension.		Figure 17-19. Thin-section of rims of marsturite crystals surrounding rhodonite cores from Franklin. Field of view is 4 mm. Smithsonian Institution, #C2485-1. Photo by Vic Krantz.

Occurrence and paragenesis

Marsturite occurs at Franklin as small 0.5 mm elongate pinacoidal crystals, associated with rhodonite, manganaxinite, and willemite. Dunn and Leavens (1986) reported a second habit, also from Franklin, of marsturite occuring as rims on rhodonite crystals, associated with manganaxinite, willemite, and ganophyllite (Figure 18-36). These colorless to light-pink serrated rims on rhodonite crystals (Figures 17-17 and 17-19) are composed of crystals, and forms can be discerned. These samples were probably preserved because of the attractiveness of the bright yellow manganaxinite, pink rhodonite, and the rare ganophyllite of uncommon habit. In recent years marsturite has been found in the Molinello Mine in Italy.

Name

Marsturite is named in honor of Mrs. E. Hadley Stuart (Marion Stuart) of Bellevue, Idaho, in recognition of her support of science, especially mineralogical research and mineral exhibits.

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Copyright © 1995 by Pete J. Dunn			Website by Herb Yeates

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