Question

what can cause the formation of idiomorphic apatite crystals in platform carbonates?​

Answer 1

Francolite synonymous with carbonate fluorapatite or

called collophane when microcrystalline

is the principal component of many sedimentary

phosphate rocks (“phosphorite”). Brushite (41.24 wt.% P2O5 ) and

monetite (52.16 wt.% P2O5) are only widespread in guano deposits,

where locally rather exotic phosphate minerals accommodating N, O

and H bridge the gap between organo-mineralic chemical compounds

and inorganic chemical compounds (coastal region in Chile). They can be the source of your apatite when recrystallized.

Marine upwelling along the shelf edge is responsible for the formation of carbonate-hosted phosphates and phosphorites. Some phosphorites accumulated within high energy — nearshore zones. Some formed in the outer shelf deposits. The common minerals besides francolite are smectite, illite, opal, sepiolite, clinoptilolite, quartz , siderite, smectite and palygorskite.

When they undergo physical-chemical alteration, e.g., an increase in T apatite may recrystallize and form XX of different X shape from elongated to stubby XX (pisms). You should investigate your apatite s.s.s. and determine how much carbon dioxide, F , Cl and OH is still in the XX. The OH- and CO3- anion complex should decrease along with increasing T. Also have a look at the minerals associated with the phosphate. The minerals mentioned above only occur in diagenetically overprinted phosphate-bearing limestones.

There are many phosphate deposits hosted by calcareous rocks.

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Answer 2

Answer: Marine upwelling along the shelf edge is responsible for the formation of carbonate-hosted phosphates and phosphorites. Some phosphorites accumulated within high energy — nearshore zones. Some formed in the outer shelf deposits. The common minerals besides francolite are smectite, illite, opal, sepiolite, clinoptilolite, quartz , siderite, smectite and palygorskite.

When they undergo physical-chemical alteration, e.g., an increase in T apatite may recrystallize and form XX of different X shape from elongated to stubby XX (pisms). You should investigate your apatite s.s.s. and determine how much carbon dioxide, F , Cl and OH is still in the XX. The OH- and CO3- anion complex should decrease along with increasing T. Also have a look at the minerals associated with the phosphate. The minerals mentioned above only occur in diagenetically overprinted phosphate-bearing limestones.

Explanation: