376:, have a lamellar habit with one well developed cleavage and two subsidiary cleavages at right angles to each other. It has an alpha of 1.7 to 1.68 and a gamma of 1.71 to 1.72 and a birefringence of 0.04. On average iddingsite has a density of approximately 2.65 g/cm and a hardness of 3 (calcite). Variability in these values are expected due to the differences in crystal structure that can occur from different stages in the alteration process.
290:
dependent on oxidation conditions, hydration and the magma from which iddingsite forms must be rich in water vapor. The alteration of olivine to iddingsite occurs in a highly oxidizing environment under low pressure and at intermediate temperatures. Temperature needed for the alteration process has to be above temperatures that could cause the olivine to solidify, but below temperatures that would cause structural reorganization.
335:
hematite-like iddingsite is as follows: a-axis of olivine is parallel to the c-axis of hematite, the b-axis of olivine is parallel to the +/− plane of hematite and the c-axis of olivine is parallel to the +/− plane of hematite. This hematite structure is very well oriented and occurs because of the high stability of the anion framework and because the cations can be made to migrate throughout the structure.
331:. Diffraction spots caused by goethite are diffuse even though the material is well oriented. These structures are aligned parallel to the original olivine with a-axis (goethite) parallel to a-axis (olivine), b-axis (goethite) parallel to b-axis (olivine) and c-axis (goethite) parallel to c-axis (olivine). The preferred orientation of olivine and goethite are when they are parallel with their z-axis.
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2.779 Å. Olivine axes are oriented in the following way: a is parallel to X-axis, b is parallel to Y-axis and c is parallel to Z-axis. X-ray diffraction patterns taken from iddingsite vary from true olivine pattern to patterns that are very diffuse spots. This is an indication of a distorted structure caused by atomic replacement creating a distorted atomic arrangement.
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hexagonal sequences of approximately close-packed oxygen sheets. These oxygen layers are perpendicular to the x-axis of an olivine cell. One of the close-packed directions is parallel to the z-axis of an olivine cell. These ion arrangements within olivine control the structural orientation of the alteration products.
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Olivine has an orthorhombic structure with a space group of Pbnm. Olivine-like structures represent the stage that breaks down olivine with chemical changes introduced by alterations. These structures have the cell dimensions a = 4.8, b = 10.3 and c = 6.0 Å, a space group Pbnm and a d-spacing of
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Silicate structures are the most variable among all of the structures discussed. A common silicate structure consists of a hexagonal array of cylinders whose length is parallel to the x-axis of the olivine and the side of the hexagonal cell is parallel to the z-axis of olivine. Diffraction effects
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Spinel structures consist of multiple oxide structures that are cubic and have cubic close packing. The spinel structures have a twined orientation and are controlled by close packed sheets. This twined orientation is can be described as: the a-axis of olivine is parallel to the (111) spinel face.
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rocks, and it is absent from deep-seated rocks. Iddingsite is an epimagmatic mineral derived during the final cooling of lava in which it occurs from a reaction between gases, water and olivine. The formation of iddingsite is not dependent on the original composition of the olivine. It is however
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The structure of iddingsite is difficult to characterize because of the complexity of the possible alterations that can occur from olivine. Iddingsite has the tendency to be optically homogeneous which indicates that there is some structural control. Structural rearrangements are controlled by
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Iddingsite is a pseudomorph, and during the alteration process the olivine crystals had their internal structure or chemical composition changed, although the external form has been preserved. This is not true for all phases of the alteration of olivine because the atomic arrangement becomes
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Hematite-like structures occur in a similar fashion as goethite. Hematite has a triangular crystal system and experiences twinning by having an approximately hexagonal close-packed oxygen framework and has a structural orientation similar to olivine. When twinning occurs, the orientation of
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Goethite-like structures are common because goethite is in the same space group as olivine. This allows for goethite to grow within the olivine making the close packed planes common for both structures. Goethite-like structures have cell dimensions a=4.6, b= 10.0 and c =
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material. The color of iddingsite varies from red-brown to orange-brown to deep ruby red to orange-red. The color of iddingsite in plane polarized light is the same until the later alteration stages when it turns into a darker color due to the strengthening effect of
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The b-axis of olivine is parallel to +/− (112) and the c-axis of olivine is parallel to +/− (110) spinel face. These alterations tend to be rare in iddingsite but when they are present they show a sharp diffraction spot making them easily identified.
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Iddingsite has been a subject researched in recent years because of its presence in the
Martian meteorites. The formation of iddingsite requires liquid water, giving scientists an estimate as to when there has been liquid
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Iddingsite is a rock that lacks a definite chemical composition, so exact compositions cannot be calculated. An approximated composition for a hypothetical end product of iddingsite has been calculated as being
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Some samples that have completed their alterations have miscellaneous cleavage thereby making it not a very good diagnostic tool. Most samples have no cleavage at all. Thin sections from an occurrence near
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distorted and causes a non-definite structure to form. Iddingsite has a composition that is constantly transforming from the original olivine passing through many stages of structural and chemical change.
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Because iddingsite is constantly transforming it does not have a definite structure or a definite chemical composition. The chemical formula for iddingsite has been approximated as MgO * Fe
360:. An increase in beta refractive index, which typically is 1.9 can be seen in most types of iddingsite, as the alteration process proceeds. Iddingsite also exhibits an increase in
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patterns found that there are five structural types of iddingsite that can occur during different stages of alteration. They are: olivine-like structures,
462:
Swindle T. D. et al. "Noble Gases in
Iddingsite from the Lafayette meteorite: Evidence for Liquid water on Mars in the last few hundred million years".
168:. As it has been found on Martian meteorites, its ages have been calculated to obtain absolute ages when liquid water was at or near the surface of
89:
561:
Borg Lars, Drake
Michaels. "A review of meteorite evidence for the timing of magmatism and of surface or near-surface liquid water on Mars".
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caused by this structure can be attributed to the formation of sheet silicate structures that have a very disordered stacking of layers.
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that has a composition that is constantly transforming from the original olivine, passing through many stages of
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and the removal of MgO (Gay and Le Maitre 1961). The chemical formula for iddingsite is approximated as MgO * Fe
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Iddingsite is a pseudomorph that usually has crystals rimmed by a thin zone of yellowish brown or greenish
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O where MgO can be substituted by CaO. The geologic occurrence of iddingsite is limited to extrusive or
478:
Ross, Shannon. "The Origin, Occurrence, Composition and
Physical Properties of the Mineral Iddingsite".
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of the meteorite samples showed that Mars had water on its surface anywhere from 1300 Ma to 650 Ma ago.
568:
Eggeton, Richard. "Formation of
Iddingsite Rims on Olivine: a Transmission Electron Microscope Study".
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O where MgO can be substituted by CaO by a ratio of 1:4. There are also some trace constituents of Na
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O. The chemical process associated with the alteration consists of the addition of Fe
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519:
Brown George. "A structural Study of
Iddingsite from New South Wales, Australia".
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O = 14%. Throughout the alteration process of olivine, there is a decrease in SiO
582:
Sun Ming Shan. "The Nature of
Iddingsite in Some Basaltic Rocks of New Mexico".
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Smith, Katherine et al. "Weathering of Basalt: Formation of
Iddingsite".
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near the surface. It is absent from deep-seated rocks and is found on
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The geologic occurrence of
Iddingsite is limited to extrusive or
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Gay Peter; Le Maitre, R. W. "Some
Observations on Iddingsite".
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O that enter iddingsite as the alteration process progresses.
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in the presence of liquid water and can be described as a
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caused it to be de-listed as an official mineral by the
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364:and dispersion as the alteration process proceeds.
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491:Edwards, Andrew. "The Formation of Iddingsite".
72:, and consists of a mixture of remnant olivine,
92:; thus, it is properly referred to as a rock.
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579:, Col. 35. No. 6, pp. 418–428, 1987.
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84:. Debates over iddingsite's non-definite
565:. Vol. 110, E12S03, pp. 1–10, 2005.
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533:David Bartholmy (31 December 2009),
237:, FeO and MgO and an increase in Al
64:that is derived from alteration of
597:Lecture at University of Wisconsin
523:. 44; 3–4, pp. 251–260, 1959.
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464:Meteoritics and Planetary Science
450:. 46; 1–2, pp. 92–111. 1961.
160:that are formed by injection of
37:Olivine weathering to iddingsite
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563:Journal of Geophysical Research
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572:, Col. 32. No. 1, 1–11, 1984.
68:. It is usually studied as a
48:Olivine, clays, ferrihydrites
179:, an American petrologist.
466:35, pp. 107–115, 2000.
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95:Iddingsite forms from the
586:. 42; pp. 7–8, 1957.
535:"Iddingsite mineral data"
495:, pp. 277–281, 1938.
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370:Lismore, New South Wales
577:Clays and Clay Minerals
570:Clays and Clay Minerals
109:macroscopically visible
584:American *Mineralogist
198:Potassium-argon dating
521:American Mineralogist
493:American Mineralogist
480:Proc. U.S. Nat., Mus.
448:American Mineralogist
539:Mineralogy database
347:Physical properties
281:Geologic occurrence
175:It was named after
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602:2007-07-12 at the
556:Additional sources
307:-like structures,
353:cryptocrystalline
301:X-ray diffraction
177:Joseph P. Iddings
158:subvolcanic rocks
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183:Introduction
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116:fine-grained
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24:Igneous rock
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358:pleochroism
229:= 62% and H
204:Composition
127:pseudomorph
123:porphyritic
78:iron oxides
43:Composition
482:, 67 1925.
403:Mindat.org
398:Iddingsite
380:References
287:hypabyssal
166:meteorites
131:structural
119:groundmass
105:phenocryst
97:weathering
55:Iddingsite
17:Iddingsite
408:March 25,
374:Australia
327:3.0
294:Structure
213:= 16%, Al
619:Minerals
613:Category
600:Archived
317:silicate
309:hematite
305:goethite
221:= 8%, Fe
112:crystals
544:19 July
273:O and K
148:* 3SiO
70:mineral
66:olivine
313:spinel
101:basalt
80:, and
265:* 4 H
245:and H
162:magma
152:* 4 H
121:of a
114:in a
57:is a
546:2012
410:2019
170:Mars
133:and
62:rock
209:SiO
99:of
90:IMA
615::
537:,
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372:,
196:.
172:.
76:,
329:Å
275:2
271:2
267:2
263:3
261:O
259:2
255:3
253:O
251:2
247:2
243:3
241:O
239:2
235:2
231:2
227:3
225:O
223:2
219:3
217:O
215:2
211:2
154:2
150:2
146:3
144:O
142:2
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