Endogangue

Endogangue includes yellow-brown to opaque humic matter of marine planktonic origin, siliciclastic grains and authigenic pyrite framboids and secondary apatite crystals.

Certain pellets are very homogeneous in appearance, with practically no endogangue; grains of this type are frequently contained in sub-outcrop strata.

The other constituents (endogangue) are goethite, attapulgite and fine quartz granules.

The exogangue is generally carbonated, showing phosphate grains surrounded by dolomite rhombohedra (Figure 1f), while the endogangue is present either as silica (Figure 1g) or carbonate grains (Figure 1h), occurring, respectively, as quartz or calcite included within the phosphate grains.