coccolith
Concise Oxford English Dictionary © 2008 Oxford University Press:
coccolith /ˈkɒkəlɪθ/
▶noun Biology a minute rounded calcareous platelet, numbers of which form the spherical shells of coccolithophores.
– origin C19: from Gk kokkos ‘grain or berry’ + lithos ‘stone’.
'coccolith' also found in these Oxford entries:

