1. An intracorporeal marker, for marking a site within living tissue of a host, comprising: a body comprised of first and second distinct materials, the body having a core region made of the first material completely surrounded by an outer region made of the second material, the first material being comprised of porous hydroxyapatite having physical properties that permit the body to be distinguished from human soft tissue under visualization using ultrasonic and radiation imaging modalities, the second material being comprised of a second hydroxyapatite, and wherein the porous hydroxyapatite of the core region has a first porosity and the second hydroxyapatite of the outer region has a second porosity, wherein the first porosity of the porous hydroxyapatite of the core region is higher than the second porosity of the second hydroxyapatite of the outer region.