Formula: KAl2(AlSi3)O10(OH,F)2 Monoclinic Description:Muscovite is a common mica, forming silvery to pale-colored flakes most commonly schists and granite pegmatites. It can survive weathering, and form sparkling grains in sands and sandstone. Muscovite. From the mineral collection of …
Sauk County
Phosphosiderite
Formula: FePO4.2H2O Monoclinic Description: Lavender-colored coatings of phosphosiderite in matrix of other black-altered phosphate minerals. From the Stewart Mine, near Pala, San Diego County, California. (Photo by W. Cordua.) Phosphosiderite forms reddish or purplish elongated to radial …
Pipestone
Formula: Mixture of pyrophillite and sericite. Description:Pipestone is a compact pink to red metamorphosed mudstone (or argillite) of a consistency that allows it to be carved into pipes and other art objects. It is found as thin …
Plagioclase
Formula: CaAl2Si2O8 Triclinic Description: Plagioclase is a family of feldspar minerals forming a solid solution that ranges, relatively continuously, from pure sodium aluminum silicate (the end member called albite) to pure calcium aluminum silicate (the end member …
Potassium Feldspar
Formula: KAlSi3O8 Monoclinic or Triclinic Description: Potassium feldspar refers to any of the three polymorphs microcline, orthoclase or sanidine. The distinction between these minerals can be made with certainty only after detailed X-Ray analysis. This has not …
Pseudorutile
Formula: Fe2Ti3O9 Description:Pseudorutile generally forms as an alteration product of ilmenite during weathering, especially in tropical environments. It has recently been documented as a mineral formed during low-grade metamorphism.SAUK COUNTY: Pseudorutile was found as tiny grains (50 …
Pyrophyllite
Formula: Al2Si4O10(OH)2 Monoclinic Description: Pyrophyllite is a micaceous mineral formed as a result of the relatively low grade metamorphism of aluminum-rich rocks. It can also form as a hydrothermal replacement of aluminous minerals such as feldspars. The …
Quartz
Formula: SiO2 Hexagonal Description: Quartz is the most abundant mineral. It is an essential component of granitic igneous rocks, of sedimentary rocks such as sandstone and chert and of metamorphic rocks such as quartzites. It is a …
Rutile
Formula: TiO2 Tetragonal Description: Rutile from the Nine Mile Pluton near Wausau in Marathon County, Wisconsin. Scanning electron microscope image. (Photo by Al Falster.) Rutile is an accessory mineral found in a wide variety of rocks, usually as …
Siderite
Formula: FeCO3 Hexagonal Description: Siderite forms as a sedimentary precipitate, in hydrothermal veins, in metamorphic rocks formed from such protoliths, and, rarely, in pegmatites. In sedimentary environments it forms in extensive beds of banded iron formations …