calcium cave stone texture textures dark carbonate iglesias Mineral minerals pisoids pisolite pisolith quarry rare samples Sardinia sulcis abstract appearance breakable broken brown calcification calcium-carbonate color colors colour colours cook cooking dried dry egg egg-shells eggs eggshells empty external food fragile fragility fragmentary fragments hard-shelled hollow idiomatic-expressions idioms inside internal leftover leftovers life outer-covering outside oval ovoid Remains scattered scattering speckled surface surfaces white yolk