640:
489:
375:
481:
20:
747:
207:
524:. Commonly, the presence of iron is determined to be within a rock due to certain colorations from oxidation. Oxidation is the loss of electrons from an element. Oxidation can occur from bacteria or by chemical oxidation. This often happens when ferrous ions come into contact with water (due to dissolved oxygen within surface waters) and a water-mineral reaction occurs. The formula for the oxidation/reduction of iron is:
323:(BIFs) were originally chemical muds and contain well developed thin lamination. They are able to have this lamination due to the lack of burrowers in the Precambrian. BIFs show regular alternating layers that are rich in iron and chert that range in thickness from a few millimeters to a few centimeters. The formation can continue uninterrupted for tens to hundreds of meters stratigraphically. These formations can contain
457:
308:
734:
263:. Most iron formations are deformed or metamorphosed simply due to their incredibly old age, but they still retain their unique distinctive chemical composition; even at high metamorphic grades. The higher the grade, the more metamorphosed it is. Low grade rocks may only be compacted while high grade rocks often can not be identified. They often contain a mixture of
589:
443:
Granular iron formations (GIFs) were originally well-sorted chemical sands. They lack even, continuous bedding that takes the form of discontinuous layers. Discontinuous layers likely represent bedforms that were generated by storm waves and currents. Any layers that are thicker than a few meters and
222:
can not be used as a way to classify iron formations because it is a common component in many types of rocks. They are well banded and the banding can be anywhere from a few millimeters to tens of meters thick. The layers have very distinct banded successions that are made up of iron rich layers that
464:
There are four facies types associated with iron-rich sedimentary rocks: oxide-, silicate-, carbonate-, and sulfide-facies. These facies correspond to water depth in a marine environment. Oxide-facies are precipitated under the most oxidizing conditions. Silicate- and carbonate-facies are
465:
precipitated under intermediate redox conditions. Sulfide-facies are precipitated under the most reducing conditions. There is a lack of iron-rich sedimentary rocks in shallow waters which leads to the conclusion that the depositional environment ranges from the
178:. Ooids can be a distinct characteristic though they are not normally a main component of ironstones. Within ironstones, ooids are made up of iron silicates and/or iron oxides and sometimes occur in alternating laminae. They normally contain
762:
under the microscope under transmitted light. Under reflected light, magnetite shows up as metallic and a silver or black color. Hematite will be a more reddish-yellow color. Pyrite is seen as opaque, a yellow-gold color, and metallic.
539:
easily and is a mild reducing agent. These compounds are more soluble because they are more mobile. Fe is the ferric form of iron. This form of iron is very stable structurally because its valence electron shell is half filled.
771:
that readily oxidizes to limonite. When it is partially or fully oxidized to limonite, the green color becomes a yellowish-brown. Limonite is opaque under the microscope as well. Chamosite is an iron silicate and it has a
780:
and it has a very high birefringence. The thin sections often reveal marine fauna within oolitic ironstones. In older samples, the ooids may be squished and have hooked tails on either end due to compaction.
567:
is often made from this process and is a major source of iron in sediments. However, once it is deposited it must be dehydrated in order to come to an equilibrium with hematite. The dehydration reaction is:
358:
BIFs are divided into type categories based on the characteristics related to the nature of their formation and unique physical and chemical properties. Some categories of banded iron formations are the
128:
sedimentary rock. Generally, they are from the
Phanerozoic which means that they range in age from the present to 540 million years ago. They can contain iron minerals from the following groups:
231:. They sometimes grade locally into chert or dolomite. They can have many different textures that resemble limestone. Some of these textures are micritic, pelleted, intraclastic, peloidal,
435:. Total iron content in this class type exceeds 10 tons. They can extend to over 10 kilometers. Deposition occurs in relatively shallow marine conditions under transgressing seas.
270:
The above classification scheme is the most commonly used and accepted, though sometimes an older system is used which divides iron-rich sedimentary rocks into three categories:
267:
and granular iron formations. Iron formations can be divided into subdivisions known as: banded iron formations (BIFs) and granular iron formations (GIFs).
46:. However, most sedimentary rocks contain iron in varying degrees. The majority of these rocks were deposited during specific geologic time periods: The
884:
Klein, Cornelis; Beukes, Nicolas J. (1993-05-01). "Sedimentology and geochemistry of the glaciogenic late
Proterozoic Rapitan Iron-Formation in Canada".
214:
Iron formations must be at least 15% iron in composition, just like ironstones and all iron-rich sedimentary rocks. However, iron formations are mainly
477:. (The diagram does not have the abyssal plain labeled, but this would be located to the far right of the diagram at the bottom of the ocean).
555:
forming process that occurs in warm and moist climates under broadleaf evergreen forests. Soils formed by laterization tend to be highly
344:
628:). It generally does not preserve detail and the pyrite forms within the structure as many microcrystals. In freshwater environments,
218:
in age which means that they are 4600 to 590 million years old. They are much older than ironstones. They tend to be cherty, though
850:, Kluwer Academic Publishers, Dordrecht, Netherlands, pp. 124–125, 130–133, 159–160, 367–368, 376–384, 486–489, 555–557, 701–702
616:
fossils. It commonly takes place in marine depositional environments where there is organic material. The process is caused by
639:
411:. Iron content in this class type rarely exceeds 10 tons. They range in thickness from 10–100 meters. Deposition occurs in
247:. The dominant minerals in the oxide facies are magnetite and hematite. The dominant minerals in the silicate facies are
391:
and Early
Proterozoic. The type is distinctive as the hydrothermal-input has notably less influence on this formation's
697:) are sulfide minerals and favor reducing conditions. They are the most common in fine-grained, dark colored mudstones.
935:
Harnmeijer, Jelte P., 2003, Banded Iron-Formations: A Continuing Enigma of
Geology, University of Washington, WA, USA
944:
Pettijohn, Potter, and Siever, 1987, Sand and
Sandstone, Springer-Verlag Publishing Inc., New York, NY, pg. 50-51
978:
Collison, J.D., 1989, Sedimentary
Structures, The University Printing House, Oxford, Great Britain, pp. 159–164
124:
Ironstones consist of 15% iron or more in composition. This is necessary for the rock to even be considered an
921:
Stow, Dorrik Av, 2005, Sedimentary Rocks in the Field, Academic press - Manson
Publishing, London, UK, p. 218
182:
debris and sometimes the fossils are partly or entirely replaced by iron minerals. A good example of this is
164:. They are typically nonbanded, however they can be very coarsely banded on occasion. They are hard and non-
58:(205 to 66 million years ago). Overall, they make up a very small portion of the total sedimentary record.
259:. The dominant mineral in the carbonate facies is siderite. The dominant mineral in the sulfide facies is
243:. In low-grade iron formations, there are different dominant minerals dependent on the different types of
103:
The accepted classification scheme for iron-rich sedimentary rocks is to divide them into two sections:
1020:
69:. They are a major source of iron and are mined for commercial use. The main iron ores are from the
636:
that has taken place within a fossil may sometimes be referred to as degree of pyritization (DOP).
493:
632:
will replace carbonate shells instead of pyrite due to the low amounts of sulfate. The amount of
183:
351:
channels. In comparison to GIFs, BIFs contain a much larger spectrum of iron minerals, have more
678:) are carbonates and favor alkaline, reducing conditions. They commonly occur as concretions in
969:
Parrish, J. Michael, 1991, The
Process of Fossilization, Belhaeven Press, Oxford, UK, pp. 95–97
144:, hematite, and magnetite. An example of a mineral in iron-rich rock containing carbonates is
324:
320:
264:
492:
Iron bacteria growing on iron-rich water seeping from a tall bluff, Sipsey
Wilderness Area,
488:
431:
Superior types are large, thick, extensive iron deposits across stable shelves and in broad
168:. The components of the rock range in size from sand to mud, but do not contain a lot of
8:
444:
are uninterrupted, are rare for GIFs. They contain sand-sized clasts and a finer grained
1025:
777:
392:
244:
901:
470:
466:
432:
133:
86:
893:
860:
759:
445:
195:
137:
39:
989:
Constituents, Textures, Cements, and
Porosities of Sandstones and Associated Rocks
560:
224:
65:. Iron deposits have been located on all major continents with the exception of
897:
605:
Pyritization is discriminatory. It rarely happens to soft tissue organisms and
416:
332:
172:. They are also more aluminous. They are not laminated and sometimes contain
1014:
905:
834:, American Geologic Institute, Ventura Publisher, Alexandria, VA, pp. 335–336
773:
512:
iron are components in many minerals, especially within sandstones. Fe is in
474:
404:
374:
328:
129:
92:
is also typically mined. A productive belt of iron formations is known as an
70:
768:
633:
513:
252:
240:
187:
480:
223:
alternate with layers of chert. Iron formations are often associates with
403:
Algoma types are small lenticular iron deposits that are associated with
340:
228:
215:
206:
47:
991:, The American Association of Petroleum Geologists, Tulsa, OK, pp. 43–45
19:
746:
711:) is usually the pigment in red beds and requires oxidizing conditions.
556:
532:
The formula works for oxidation to the right or reduction to the left.
521:
412:
256:
248:
153:
148:
and an example of minerals in an iron-rich rock containing silicate is
66:
24:
814:(4th ed.), Pearson Education Inc., Upper Saddle River, NJ, pp. 217–223
588:
302:
764:
690:
683:
606:
408:
336:
296:
279:
236:
161:
149:
140:. Some examples of minerals in iron-rich rocks containing oxides are
119:
82:
51:
456:
754:
volcanic rock showing an oxidized iron matrix (orange/brown color).
751:
714:
700:
679:
668:
653:
629:
564:
548:
536:
517:
387:
Rapitan types are associated with the glaciogenic sequences of the
272:
145:
141:
89:
78:
74:
62:
55:
729:
O) is used for unidentified massive hydroxides and oxides of iron.
617:
613:
505:
388:
348:
28:
733:
448:, and generally belong to the oxide or silicate mineral facies.
621:
609:
509:
395:(REE) chemistry than other formations during this time period.
260:
232:
179:
169:
620:
reduction which replaces carbonate skeletons (or shells) with
520:
in small amounts. Fe is in oxides, hydrous, anhydrous, and in
307:
186:. They are smaller in size and less likely to be deformed or
352:
292:
219:
165:
157:
552:
535:
Fe is the ferrous form of iron. This form of iron gives up
420:
174:
43:
288:
54:(539 to 419 million years ago), and the middle to late
1004:, William Clowes Ltd., Essex, Great Britain, pp. 78–81
1000:
Adams, A.E., MacKenzie, W.S., and Guilford, C., 1984,
960:, Blackwell Publishing, Malden, MA, pp. 20–21, 70–73
378:
Superior type banded iron formation, North America.
303:
Banded iron formations vs. granular iron formations
741:
61:Iron-rich sedimentary rocks have economic uses as
484:Water colored by oxidized iron, Rio Tinto, Spain.
16:Sedimentary rocks containing 15 wt.% or more iron
1012:
1002:Atlas of Sedimentary Rocks Under the Microscope
848:Encyclopedia of Sediments and Sedimentary Rocks
460:Profile illustrating the shelf, slope and rise.
311:Banded iron formation close up, Upper Michigan.
287:. A bog-iron deposit is iron that formed in a
194:is occasionally used to describe an ironstone
643:Oolitic Hematite, Clinton, Oneida County, NY.
931:
929:
927:
812:Principles of Sedimentology and Stratigraphy
883:
842:
840:
516:, carbonates, sulfides, and is even within
451:
438:
50:(3800 to 539 million years ago), the early
924:
846:Middleton, Gerard V. (and others), 2003,
826:
824:
822:
820:
315:
972:
952:
950:
938:
837:
745:
732:
638:
587:
487:
479:
455:
373:
306:
205:
18:
981:
963:
806:
804:
802:
800:
798:
796:
794:
1013:
917:
915:
817:
994:
947:
500:
958:Sedimentology and Sedimentary Basins
791:
912:
152:. They are often interbedded with
13:
201:
14:
1037:
98:
647:
612:are more susceptible to it than
426:
190:than iron formations. The term
776:of almost zero. Siderite is an
742:Iron–rich rocks in thin section
600:
543:
382:
355:facies, and are more abundant.
877:
853:
398:
42:which contain 15 wt.% or more
1:
784:
227:, quartz-rich sandstone, and
113:
7:
767:is an olive-green color in
758:Magnetite and hematite are
36:Iron-rich sedimentary rocks
10:
1042:
898:10.2113/gsecongeo.88.3.542
117:
830:Jackson, Julia A., 1997,
494:Bankhead National Forest
452:Depositional environment
439:Granular iron formations
861:"Banded iron formation"
295:through the process of
987:Scholle, Peter, 1979,
810:Boggs Jr., Sam, 2006,
755:
738:
644:
597:
497:
485:
461:
379:
325:sedimentary structures
321:Banded iron formations
316:Banded iron formations
312:
265:banded iron formations
211:
32:
749:
736:
642:
591:
491:
483:
459:
377:
310:
209:
22:
956:Leeder, Mike, 2006,
832:Glossary of Geology
559:with high iron and
160:, and fine-grained
756:
739:
645:
598:
501:Chemical reactions
498:
486:
462:
419:and intracratonic
393:Rare Earth Element
380:
313:
212:
33:
1021:Sedimentary rocks
865:www.sandatlas.org
471:continental slope
467:continental shelf
40:sedimentary rocks
1033:
1005:
998:
992:
985:
979:
976:
970:
967:
961:
954:
945:
942:
936:
933:
922:
919:
910:
909:
886:Economic Geology
881:
875:
874:
872:
871:
857:
851:
844:
835:
828:
815:
808:
750:Thin section of
677:
666:
1041:
1040:
1036:
1035:
1034:
1032:
1031:
1030:
1011:
1010:
1009:
1008:
999:
995:
986:
982:
977:
973:
968:
964:
955:
948:
943:
939:
934:
925:
920:
913:
882:
878:
869:
867:
859:
858:
854:
845:
838:
829:
818:
809:
792:
787:
744:
737:Limonite, USGS.
728:
724:
720:
710:
706:
696:
676:
672:
665:
661:
657:
650:
627:
603:
583:
579:
575:
561:aluminium oxide
546:
503:
454:
441:
429:
417:back arc basins
401:
385:
318:
305:
285:iron formations
204:
202:Iron formations
122:
116:
109:iron formations
101:
17:
12:
11:
5:
1039:
1029:
1028:
1023:
1007:
1006:
993:
980:
971:
962:
946:
937:
923:
911:
892:(3): 542–565.
876:
852:
836:
816:
789:
788:
786:
783:
778:iron carbonate
743:
740:
731:
730:
726:
722:
718:
712:
708:
704:
698:
694:
687:
674:
663:
659:
649:
646:
625:
602:
599:
586:
585:
581:
577:
573:
572:2 FeO(OH) → Fe
545:
542:
530:
529:
502:
499:
453:
450:
440:
437:
428:
425:
405:volcanic rocks
400:
397:
384:
381:
333:graded bedding
317:
314:
304:
301:
203:
200:
118:Main article:
115:
112:
100:
99:Classification
97:
73:consisting of
23:Iron ore from
15:
9:
6:
4:
3:
2:
1038:
1027:
1024:
1022:
1019:
1018:
1016:
1003:
997:
990:
984:
975:
966:
959:
953:
951:
941:
932:
930:
928:
918:
916:
907:
903:
899:
895:
891:
887:
880:
866:
862:
856:
849:
843:
841:
833:
827:
825:
823:
821:
813:
807:
805:
803:
801:
799:
797:
795:
790:
782:
779:
775:
774:birefringence
770:
766:
761:
753:
748:
735:
716:
713:
702:
699:
692:
688:
685:
681:
670:
655:
652:
651:
648:Iron minerals
641:
637:
635:
631:
623:
619:
615:
611:
608:
595:
590:
571:
570:
569:
566:
562:
558:
554:
550:
541:
538:
533:
527:
526:
525:
523:
519:
515:
511:
507:
495:
490:
482:
478:
476:
475:abyssal plain
472:
468:
458:
449:
447:
436:
434:
427:Superior type
424:
422:
418:
414:
410:
406:
396:
394:
390:
376:
372:
370:
369:Superior type
366:
362:
356:
354:
350:
346:
342:
338:
334:
330:
329:cross-bedding
326:
322:
309:
300:
298:
294:
290:
286:
282:
281:
276:
274:
268:
266:
262:
258:
254:
250:
246:
242:
241:stromatolitic
238:
234:
230:
226:
221:
217:
208:
199:
197:
193:
189:
188:metamorphosed
185:
181:
177:
176:
171:
167:
163:
159:
155:
151:
147:
143:
139:
135:
131:
127:
121:
111:
110:
106:
96:
95:
91:
88:
84:
80:
76:
72:
68:
64:
59:
57:
53:
49:
45:
41:
37:
30:
26:
21:
1001:
996:
988:
983:
974:
965:
957:
940:
889:
885:
879:
868:. Retrieved
864:
855:
847:
831:
811:
769:thin section
757:
658:Ca(Mg,Fe)(CO
634:pyritization
604:
601:Pyritization
593:
549:Laterization
547:
544:Laterization
534:
531:
504:
463:
442:
430:
402:
386:
383:Rapitan type
368:
364:
361:Rapitan type
360:
357:
341:ripple marks
319:
284:
278:
271:
269:
253:minnesotaite
213:
191:
184:pyritization
173:
125:
123:
108:
104:
102:
93:
60:
35:
34:
689:Pyrite and
528:Fe ↔ Fe + e
522:glauconites
399:Algoma type
365:Algoma type
229:black shale
216:Precambrian
94:iron range.
71:oxide group
48:Precambrian
1015:Categories
870:2020-03-29
785:References
684:siltstones
607:aragonitic
592:Pyritized
496:, Alabama.
469:and upper
413:island arc
409:turbidites
367:, and the
345:mud cracks
337:load casts
280:ironstones
257:glauconite
249:greenalite
162:sandstones
154:limestones
134:carbonates
114:Ironstones
105:ironstones
67:Antarctica
25:Kryvyi Rih
1026:Iron ores
906:1554-0774
765:Chamosite
691:marcasite
680:mudstones
594:Lytoceras
563:content.
557:weathered
537:electrons
518:feldspars
297:oxidation
237:pisolitic
192:iron ball
150:chamosite
138:silicates
126:iron-rich
120:Ironstone
87:carbonate
83:magnetite
63:iron ores
52:Paleozoic
752:rhyolite
715:Limonite
701:Hematite
669:siderite
654:Ankerite
630:siderite
565:Goethite
275:deposits
273:bog iron
225:dolomite
210:Bog ore.
146:siderite
142:limonite
90:siderite
79:goethite
75:hematite
56:Mesozoic
618:sulfate
614:calcite
610:fossils
506:Ferrous
473:to the
423:zones.
389:Archean
353:reduced
349:erosion
233:oolitic
29:Ukraine
904:
760:opaque
667:) and
622:pyrite
510:ferric
446:matrix
433:basins
363:, the
347:, and
283:, and
261:pyrite
255:, and
245:facies
239:, and
196:nodule
180:fossil
170:silica
166:cherty
158:shales
136:, and
130:oxides
85:. The
81:, and
551:is a
327:like
293:swamp
220:chert
175:ooids
902:ISSN
717:(2Fe
693:(FeS
682:and
673:FeCO
624:(FeS
553:soil
514:clay
508:and
421:rift
407:and
107:and
44:iron
38:are
894:doi
725:·3H
703:(Fe
580:+ H
291:or
289:bog
1017::
949:^
926:^
914:^
900:.
890:88
888:.
863:.
839:^
819:^
793:^
371:.
343:,
339:,
335:,
331:,
299:.
277:,
251:,
235:,
198:.
156:,
132:,
77:,
27:,
908:.
896::
873:.
727:2
723:3
721:O
719:2
709:3
707:O
705:2
695:2
686:.
675:3
671:(
664:2
662:)
660:3
656:(
626:2
596:.
584:O
582:2
578:3
576:O
574:2
415:/
31:.
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