PLAGIONITE
PLAGIONITE Plagionite – Pb5Sb8S17 – is a very rare sulfosalt that occurs in hydrothermal vein deposits, especially in Pb-Zn veins. It is part of Pb-Sb-Ag-Zn ores. It is classified in the Plagionite Group and may contain Ag as an impurity. 1. Characteristics Crystal system: Monoclinic prismatic. Color: Dark lead gray (“blackish”) […]
PYROCHLORE
PYROCHLORE Pyrochlore – A2Nb2(O,OH)6Z (A = Na, Ca, Sn2+, Sr, Pb2+, Sb3+, Y, U4+, H2O or a vancancy; Z = OH, F, O, H2O or a vacancy) – is a fairly rare oxide, occurring in very specific parageneses. It is the main ore of niobium. The world’s largest Nb producers mine pyrochlore. The CBMM deposit in […]
PREHNITE
PREHNITE Prehnite – Ca2(Al,Fe)Al2Si3O10(OH)2 – is a rarer inosilicate (Strunz) or phyllosilicate (Dana), typical of some more restricted parageneses. It has some economic importance as a decorative stone and gemstone. There is a pink variety, patricianite, which contains inclusions of chlorite and native copper. Prehnite may contain Fe, Mg, Na, Ti, K, and H2O as […]
PHLOGOPITE
PHLOGOPITE Phlogopite – K2Mg6Al2Si6O20(OH,F)4 – is a rarer phyllosilicate, but relatively common in parageneses with carbonates. It is an important industrial mineral. It is the second most mined mica, after muscovite. Phlogopite is part of the biotite series, which consists of: phlogopite (Fe 0-20%, Mg 100-80%), meroxene (Fe 20-50%, Mg 80-50%), lepidomelane (Fe 50-80%, Mg […]
PIEMONTITE
PIEMONTITE Piemontite – Ca2(Al,Mn3+,Fe3+)3O(Si2O7)(SiO4)(OH) – is a sorosilicate with a very restricted distribution. It has no economic importance. Piemontite is one of the members of the Epidote Group. It can contain Na, K, Fe, Ti and H2O and there is a variety with Sr. In many cases, a deep red variety of epidote, containing Mn3+, […]
PARAREALGAR
PARAREALGAR See “ORPIMENT”
PYROLUSITE
PYROLUSITE Pyrolusite – Mn4+O2 – is an oxide that constitutes one of the most important Mn ore minerals. In manganese mining, a term used is “wad”, attributed to a mixture of manganese minerals formed by submicroscopic grains mainly of pyrolusite and psilomelane. Pyrolusite is classified in the Rutile Group and is trimorphic with akhtenskite and […]
PSEUDOLEUCITE
PSEUDOLEUCITE Pseudoleucite is a pseudomorph of nepheline + orthoclase over the original leucite. The typical cubic form of leucite, the trapezohedron, may be preserved, but generally only rounded forms are observed. Leucite is typical of K-rich and silica-deficient volcanic rocks, almost exclusively occurring as phenocryst in undersaturated (mafic and alkaline) volcanic and hypabyssal rocks, such […]
POLLUCITE
POLLUCITE Pollucite – (CsNa)2(Al2Si4O12).2H2O – is a very rare tectosilicate that occurs in lithiniferous granitic pegmatites and constitutes the most important ore of Cs. Cesium is important to the oil industry. It is classified in the Zeolite Group and is part of the Analcime-Pollucita series, constituting the Cs analogue of analcime (of Na), with which […]
PSILOMELANE
PSILOMELANE Psilomelane – general formula: (Ba,H2O)2Mn5O10 – does not designate a mineral species. It is an old term, nowadays less used, referring to a set of black, hard and hydrated oxides of manganese that can contain Ba, Cu, Co, Ni, Mg, Ag, Ca, W and K. It is a mining term, very practical, used when […]