Volcanic bomb from near Flagstaff, Arizona

Basaltic eruptions normally include the ejection of globs of magma, that initially are dough-like (i.e., viscous) and full of escaping gas. I picture the globs as pizza dough. During their brief flight, the globs can wrap themselves into spindle shaped masses, called 'bombs,' and achieve best aerodynamics.

I collected this in 1973 near Flagstaff in the San Francisco Peaks region while directing field camp for the University of Arizona.  What I like best about it is its internal galaxy of rotation, giving a sense for how it spun during flight.  Furthermore, I'm impressed with the thousands of vesicles representing escaping of gas.

Age & Formation
Less than 1 million years.