Rock of the Day

Today, I will feature a close-up of one Lake Superior
rock.  Once my stones find their new home with me,
they usually become part of a larger landscape.
Occasionally I will pause to ask, "Why did I choose
this rock among thousands?"  With this stone, I
know.  It was the striations within the rock that
made it a favorite.  Ah!  to be a geologist....Can any
of you help me understand??  Obviously the striations
are another kind of rock as it is in ridges against the
mother rock.  Can any of you tell a story for me........