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Typical Minerals
Scoria has cooled too quickly for minerals to form; i.e. it is volcanic glass. Chemical composition, however, will be from either the middle or top of Bowen's Reaction series (i.e. intermediate or mafic). It is not possible to tell the composition from external appearance alone and so we just spread all scoria across the intermediate to mafic range. If we found it in place it would most likely have the composition of the surrounding rock.
     There is no scale in this picture, but the view is about 2 inches across. The very fine vesicles (holes) can be seen even here. The rock is quite light in weight since it is mostly made of holes. The next specimen has much larger vesicles in it.
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Tectonic Association
      Scoria is associated with intermediate and mafic volcanic processes in terrestrial environments, commonly appearing with vesicular basalts in cinder cones and lava flows. By itself there is not a lot we can say about the tectonic origins of this specimen, just the specific processes of gas escape and rapid cooling.
   Tectonic Cross Section - pdf version

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