A Geoscience Digital Image Library

TitleFerruginous argillite (mudstone), Missoula, Montana
DescriptionThis rock might be termed a mudstone, a term used for fine grained rocks composed of subequal amounts of quartz and clay, and lacking the texture of a shale. Although no minerals can be identified in hand specimen, microscope examination confirms the presence of quartz and clays. This specimen is labelled a “ferruginous argillite” in the Ward’s Collection of Classic North American Rocks. Translated that means it is an iron-bearing rock containing clay minerals. Sedimentary geologists might consider this a metamorphic rock, but metamorphic geologists would consider it a sedimentary rock because metamorphic fabric and minerals are very poorly developed, if at all. The sample is 9 cm across.
LocationUSA ▹ Montana. Near Missoula.
PhotographerMike Davis. 2001-04-26.
CollectionWard’s University Rock Collection #200.
Key wordsferruginous, argillite, Montana
Tech details644 KB. Hand specimen. Fujifilm FinePix S1Pro digital camera, 60mm Nikon AF micro lens.
GeoDIL number438