Pulp stones of human teeth usually contain biological apatite. In the
dental pulp of a cow, aged 12 years, we observed spherulitic pulp ston
es, up to similar to 200 mu m in diameter, consisting of radially arra
nged crystals with several kinds of light microscopy and scanning elec
tron microscopy including the secondary electron and the backscattered
electron signals. The crystals extending fan-like towards the periphe
ry showed a rectangular shape, and they had subunits of elongated crys
tallites and fine slits of NaOCl-dissolved substances, probably includ
ing organic matter and amorphous mineral. By using energy-dispersive X
-ray microanalysis, large amounts of Ca and P, and trace elements of N
a, Mg, Cl, and Fe were detected from the stones. The calcium phosphate
crystals were identified as biolgical brushite by shape, Ca/P molar r
atio, and electron diffraction pattern. Core regions of the stones con
taining granular structures, probably erythrocytes, were always presen
t in blood vessels, and rectangular crystals frequently penetrated the
vessel walls. Under the decalcified sections, the nidi were completel
y or incompletely dissolved, but the peripheries showed a radial arran
gement of erythrocytes. Thus, the nidi may be thrombus or necrotic blo
od cells including erythrocytes. Such calcospherulites in the dental p
ulp of a cow were similar to the spherulitic pulp stones in human deci
duous teeth reported previously, however, their nidi were present in d
ifferent regions.