A contribution to the crystal chemistry of ellestadite and the silicate sulfate apatitest
A series of calcium silicate sulfate apatites from Crestmore, California, which contain the coupled substitution Silvsvl for 2Pv, has been investigated using electron microprobe, powder diffraction, and single-crystal diffraction methods. Chemical analysis of eighteen specimens of different phosphorus contents proves that the Si: S ratio is essentially I : I and yields the idealized general formula Caro(SiOn):-*(SO4)3-^@O4)2.(OH,F,CD2, where x : 0 to 3. The members of this series for which x : 0 and 3l2 have been labelled "ellestadite" and "wilkeite", respectively, by previous workers. "Ellestadite" is actually a solid solution involving the end-members Cale(SiO a,){SOq)tZz, where Z: OH (hydroxylellestadite), F (fluorellestadite), or Cl (chlorellestadite). The term ellestadite is redefined to make it a group name for all compositions having >(Si,S) > P. Wilkeite is not a valid mineral species, since it is only one of many solid solutions involving the six end-members fluorapatite, hydroxyapatite, chlorapatite, fluorellestadite, hydroxylellestadite, and chlorellestadite. Although natural hydroxylellestadite is monoclinic, precession photographs of type "ellestadite" and "wilkeite" show hexagonal symmetry and no evidence of Si-S ordering as suggested by the Si: S ratio of I : I . The silicate sulfate apatites from Crestmore show a strong linear relationship between their P and F contents, such that these two variables simultaneously go to zero. Linear relationships also exist between their unit cell parameters and their P, F, and (Si+S) contents. These correlations imply a convergence of the Crestmore apatite series towards a hypothetical memberof composition Caro(SiOa)r (SO4)3(OH,CI)z and cell constants a:9.543 and c = 6.9174.
Title: Crystallization induced Sulfur and REE zoning in apatite: the example of the Colli Albani’s magmatic system Running title: Zoning in apatite from the Colli Albani
We investigate the distribution of major and trace elements in apatite crystals hosted in granular alkaline rocks composed mainly of leucite and clinopyroxene, representative of the hypabyssal crystallization of a magma body in the Colli Albani Volcanic District (CAVD). The Colli Albani is a Quaternary ultra-potassic district that was emplaced into thick limestone units along the Tyrrhenian margin of Italy. Results show that the analyzed crystals are the SrO-richest (up to 4.6 wt.%) fluorapatite (F = 2.6-3.7 wt.%) of the Italian alkaline rocks. The strontium enrichment is caused by the lack of other Sr-compatible mineral phases, such as plagioclase, alkali feldspar, and melilite in the mineralogical assemblage of these leuciteand clinopyroxene-bearing rocks and by Sr assimilation from the carbonate wall rock. The studied samples show core-rim zoning with rims enriched in Si, S, and REE whereas the cores are enriched in Ca and P. The LREE-oxides contents of apatite, reaching up to 4.2 wt.%, represent more than 95% of total REE budget, SiO2 contents range from 1.3 to 3.6 wt.%, and SO3 concentrations are between 0.6 and 1.4 wt.%. We support the idea that the REE and sulfur enrichments are a response to the crystallization caused by the pressure drop in the magmatic system during the eruption and follow the substitution mechanisms Si4+ + REE3+ = P5+ + Ca2+ and S6+ + Si4+ = 2P5+. These results also suggest the presence of the substitution Th4+ + 2Si4+ = Ca2+ + 2P5+.
The Inca Occupation of the South Coast of Peru
like the others, however; it forks into several nearly parallel ravines of which the largest are Huayuri, Rio Grande-Palpa, Ingenio (called Collao in ancient times), Nasca proper (the ancient Caxamarca), Taruga, and Poroma. Due to peculiarities of the local topography, the irrigated areas in Ica and the ravines of Nasca are located inland, at the foot of the mountains, rather than at the mouths of the rivers as is more usual in Peruvian coastal valleys. No sharp natural or cultural boundary separates the valley of Chincha from the valleys of Cafiete (ancient Huarco and Runahuana), Asia, and Mala, the next valleys going up the coast to the northwest. At the other end of the area we are considering, however, there is a sharp break; beyond Yauca the Andean foothills reach out to the sea, natural conditions are quite different, and there are important differences in the archaeological picture as well. The historical sources which mention the south coast are not particularly helpful, except in so far as they provide us with a few dates. To begin with, no chronicler gives an explicit account of the political organization of the south coast at the time it came into contact with the Incas. It can, perhaps, be inferred from Cabello Balboa's statements about common policy toward the Inca invaders that there was some sort of political connection between the valleys of Mala, Cafiete, and Chincha, but the connection need have been no more than a temporary military alliance. Cabello makes no mention at all of Pisco. The valleys of Ica, Nasca, and 125