earth science

Iddingsite

Iddingsite is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Iddingsite rather than just read about it. In short: Iddingsite is a microcrystalline rock that is derived from alteration of olivine. It is usually studied as a mineral, and consists of a mixture of remnant olivine, clay minerals, iron oxides, and ferrihydrites.

Key takeaways

Iddingsite belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Iddingsite to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Iddingsite from memory before moving on to harder problems.

Reference excerpt

Iddingsite is a microcrystalline rock that is derived from alteration of olivine. It is usually studied as a mineral, and consists of a mixture of remnant olivine, clay minerals, iron oxides, and ferrihydrites. Debates over iddingsite's non-definite crystal structure caused it to be de-listed as an official mineral by the IMA; thus, it is properly referred to as a rock. Iddingsite forms from the weathering of basalt in the presence of liquid water and can be described as a phenocryst, i.e. it has macroscopically visible crystals in a fine-grained groundmass of a porphyritic rock. It is a pseudomorph that has a composition that is constantly transforming from the original olivine, passing through many stages of structural and chemical change to create a fully altered iddingsite. 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 * Fe2O3 * 3SiO2 * 4 H2O where MgO can be substituted by CaO. The geologic occurrence of iddingsite is limited to extrusive or subvolcanic rocks that are formed by injection of magma near the surface. It is absent from deep-seated rocks and is found on meteorites. 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 Mars. It was named after Joseph P. Iddings, an American petrologist.

Introduction 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 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. 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 water on Mars. Potassium-argon dating of the meteorite samples showed that Mars had water on its surface anywhere from 1300 Ma to 650 Ma ago.

Composition 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 SiO2 = 16%, Al2O3 = 8%, Fe2O3 = 62% and H2O = 14%. Throughout the alteration process of olivine, there is a decrease in SiO2, FeO and MgO and an increase in Al2O3 and H2O. The chemical process associated with the alteration consists of the addition of Fe2O3 and the removal of MgO (Gay and Le Maitre 1961). The chemical formula for iddingsite is approximated as MgO * Fe2O3 * 4 H2O where MgO can be substituted by CaO by a ratio of 1:4. There are also some trace constituents of Na2O and K2O that enter iddingsite as the alteration process progresses.

Geologic occurrence The geologic occurrence of Iddingsite is limited to extrusive or hypabyssal 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 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.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Iddingsite

Start with the simplest possible case. Write down what Iddingsite claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Iddingsite before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Iddingsite ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Iddingsite

In research: Iddingsite appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Iddingsite in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Iddingsite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Minerals, so understanding it makes those chapters shorter.
In everyday life: Look for Iddingsite outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Iddingsite in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Iddingsite means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Iddingsite out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Iddingsite in simple terms?

Why does Iddingsite matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Iddingsite?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Iddingsite.