THE MINERAL FERTILIZERS 201
combined with a molecule of either calcium fluoride in fluorapatite,
or of calcium chloride in chlor-apatite, or of lime in
voelckerite, a species named by A. F. Rogers in 1912 after
the agricultural chemist who established its existence. Apatite
is usually present in igneous rocks to the amount of about
6 parts in the thousand, or about -I per cent. of phosphorus.
ApaTiTE VEINsS—Apatite may be dissolved from deeplying
rocks, and when the solution cools near the surface
the phosphate of lime is deposited in pockets or veins. Some
apatite veins have been regarded as igneous dykes such as
those near Ottawa in Canada and the Nelsonite “dykes”
in Virginia. The apatite veins in gneiss near Ottawa are of
gS /
I 2 ree iii
2, PC .
A
Wg
A
St
F16. 53.—PHOSPHATE FORMATION.
Diagrammatic section illustrating phosphate formation. The phosphate
is black. Gr., granitic rock with phosphatic masses associated with
pegmatites; V, apatite veins in granite and in slate, S$; B, beds with
bones and coprolites, from which the underlying limestone is converted
to phosphate; PC, granular phosphate, giving rise to phosphatic
chalks and granular phosphates by concentration by ocean
currents, represented by the arrows; C, concretionary phosphate
formed on sea floor; A, coral island with limestone phosphatized
from guano; AP, volcanic island with banks of guano which form
aluminium phosphate; VP, volcanic pipe; SL, sea-level.
pneumatolytic origin and due to deep-seated solutions of
phosphoric acid. That the Nelsonite (an apatite-ilmenite
rock) in syenite and gneiss in Virginia is not intrusive is held
by G. R. Mansfeld (Phosph. Res. U.S., 2nd Pan-Amer. Sci.
Congr., vii, 1917, p. 731).
Guano—The organic formation of phosphate depends on
the destruction of apatite by weathering and the removal
of its phosphoric acid by rivers to the sea. Some marine
animals, such as crabs and the Brachiopod, Lingula, secrete
shells of phosphate of lime. Phosphoric acid is also extracted
from sea-water by minute plants and animals;
they are the food of larger creatures, which are eaten by still
