Ilmenite

Key takeaways

Ilmenite 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 Ilmenite to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Ilmenite from memory before moving on to harder problems.

Reference excerpt

Ilmenite is a titanium-iron(II) oxide mineral with the idealized formula FeTiO3. It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used as white pigment in paints, printing inks, fabrics, plastics, paper, sunscreen, food and cosmetics.

Structure and properties Ilmenite is a heavy (specific gravity 4.7), moderately hard (Mohs hardness 5.6 to 6), opaque black mineral with a submetallic luster. It is almost always massive, with thick tabular crystals being quite rare. It shows no discernible cleavage, breaking instead with a conchoidal to uneven fracture. Ilmenite crystallizes in the trigonal system with space group R3. The ilmenite crystal structure consists of an ordered derivative of the corundum structure; in corundum all cations are identical but in ilmenite Fe2+ and Ti4+ ions occupy alternating layers perpendicular to the trigonal c axis. Pure ilmenite is paramagnetic (showing only very weak attraction to a magnet), but ilmenite forms solid solutions with hematite that are weakly ferromagnetic and so are noticeably attracted to a magnet. Natural deposits of ilmenite usually contain intergrown or exsolved magnetite that also contribute to its ferromagnetism. Ilmenite is distinguished from hematite by its less intensely black color and duller appearance and its black streak, and from magnetite by its weaker magnetism.

Discovery In 1791, William Gregor discovered a deposit of black sand in a stream that runs through the valley just south of the village of Manaccan (Cornwall), and identified for the first time titanium as one of the constituents of the main mineral in the sand. Gregor named this mineral manaccanite. The same mineral was found in the Ilmensky Mountains, near Miass, Russia, and named ilmenite.

Mineral chemistry Pure ilmenite has the composition FeTiO3. However, ilmenite most often contains appreciable quantities of magnesium and manganese and up to 6 wt% of hematite, Fe2O3, substituting for FeTiO3 in the crystal structure. Thus the complete chemical formula can be expressed as (Fe,Mg,Mn,Ti)O3. Ilmenite forms a solid solution with geikielite (MgTiO3) and pyrophanite (MnTiO3) which are magnesian and manganiferous end-members of the solid solution series. Although ilmenite is typically close to the ideal FeTiO3 composition, with minor mole percentages of Mn and Mg, the ilmenites of kimberlites usually contain substantial amounts of geikielite molecules, and in some highly differentiated felsic rocks ilmenites may contain significant amounts of pyrophanite molecules. At temperatures above 950 °C (1,740 °F), there is a complete solid solution between ilmenite and hematite. There is a miscibility gap at lower temperatures, resulting in a coexistence of these two minerals in rocks but no solid solution. This coexistence may result in exsolution lamellae in cooled ilmenites with more iron in the system than can be homogeneously accommodated in the crystal lattice. Ilmenite containing 6 to 13 percent Fe2O3 is sometimes described as ferrian ilmenite. Ilmenite alters or weathers to form the pseudo-mineral leucoxene, a fine-grained yellowish to grayish or brownish material enriched to 70% or more of TiO2. Leucoxene is an important source of titanium in heavy mineral sands ore deposits.

Paragenesis Ilmenite is a common accessory mineral found in igneous and high-grade metamorphic rocks. It is found in large concentrations in layered intrusions where it forms as part of a cumulate layer within the intrusion. Ilmenite generally occurs in these cumulates together with orthopyroxene or in combination with plagioclase and apatite (nelsonite). Magnesian ilmenite is formed in kimberlites as part of the MARID association of minerals (mica-amphibole-rutile-ilmenite-diopside) assemblage of glimmerite xenoliths. Manganiferous ilmenite is found in granitic rocks and also in carbonatite intrusions where it may also contain anomalously high amounts of niobium. Many mafic igneous rocks contain grains of intergrown magnetite and ilmenite, formed by the oxidation of ulvospinel.

Processing and consumption

Most ilmenite is mined for titanium dioxide production. Ilmenite and titanium dioxide are used in the production of titanium metal. Titanium dioxide is most used as a white pigment, and the major consuming industries for TiO2 pigments are paints and surface coatings, plastics, and paper and paperboard. Per capita consumption of TiO2 in China is about 1.1 kilograms per year, compared with 2.7 kilograms for Western Europe and the United States.

Titanium is the ninth most abundant element on Earth and represents about 0.6 percent of the Earth's crust. Ilmenite is commonly processed to obtain a titanium concentrate, which is called "synthetic rutile" if it contains more than 90 percent TiO2, or more generally "titaniferous slags" if it has a lower TiO2 content. More than 80 percent of the estimated global production of titanium concentrate is obtained from the processing of ilmenite, while 13 percent is obtained from titaniferous slags and 5 percent from rutile. Ilmenite can be converted into pigment-grade titanium dioxide via either the sulfate process or the chloride process. Ilmenite can also be improved and purified to titanium dioxide in the form of rutile using the Becher process. Ilmenite ores can also be converted to liquid iron and a titanium-rich slag using a smelting process. Steelmakers use ilmenite ore as a flux to line the blast furnace hearth refractory. Ilmenite can be used to produce ferrotitanium via an aluminothermic reduction.

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Illustrations

Worked examples

Example 1 — a first encounter with Ilmenite

Start with the simplest possible case. Write down what Ilmenite 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 Ilmenite 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 Ilmenite 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 Ilmenite

In research: Ilmenite 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 Ilmenite 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: Ilmenite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Ilmenite group, Iron(II) minerals, Magnetic minerals, so understanding it makes those chapters shorter.
In everyday life: Look for Ilmenite 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.

How to study Ilmenite in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Ilmenite 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 Ilmenite out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Ilmenite in simple terms?

Ilmenite is a titanium-iron(II) oxide mineral with the idealized formula FeTiO3. It is a weakly magnetic black or steel-gray solid.

Why does Ilmenite 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 Ilmenite?

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 Ilmenite.