The “Black Rock Desert”, due west of Fillmore in west-central Utah’s Sevier Desert, has some nice basalt lava flows.  The rocks shown below are from there - these represent Holocene-aged Fillmore Craters volcanics (<10,000 years old).  The lavas are pretty rough & jagged.  The rocks themselves range from lightweight scoriaceous basalts to heavier vesicular basalts.  The surface morphologies of the scorias show that many formed by stretching of sticky lava during cooling - this can be seen at active aa lava fronts in Hawaii.


Stretched scoriaceous basalt (7.0 cm across)


Stretched scoriaceous basalt (above & below) (above: longest dimension 9.2 cm; below: field of view ~4.0 cm across)



Some Fillmore Craters volcanic rocks are parts of lava tubes.  Many basaltic lava fields in western America have well developed, small to large lava tubes.  The ceilings of the lava tubes often have a “bloopey” appearance to them.  These are lavacicles - they hang down from the ceiling and have a distinctive chocolate batter-like sheen.


Vesicular basalt - cross-section of a lava tube ceiling. 


Lavacicles and vesicular basalt (above & below; field of view ~8.5 cm across) from the interior surface of a basalt lava tube ceiling.



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