Every now and then, a stone really stands out. This one isn’t from anywhere near Oakland, but somehow it wound up in a low wall in the front yard of a house on Pleasant Valley Court. My fellow geobloggers and geotwitterers think it must be tourmaline crystals. Click it for a larger version.
“Exotic blocks” is a phrase used in the research community for bodies of land that seem to have traveled from elsewhere to their present location.
Oakland Geology 
23 April 2009 at 9:32 pm
Almost certainly pink tourmaline (elbaite) in quartz/albite matrix. Lithium-boron rich granitic pegmatites that produce this stuff are pretty much unknown in Northern California, but common in some parts of the Peninsular Ranges Batholith in San Diego County and Baja del Norte. Someone must have brought it home from a field trip to decorate the yard, like I have.