Occurrence of transition elements

How do the transition elements occur in nature?

In plain words: how a metal is found depends on how reactive it is. Gold barely reacts, so it lies in the ground as gold. Iron combines readily with oxygen, so in the crust it is found combined, mostly as oxides, and we have to dig those up and reduce them to the metal.

NCERT’s Class 12 chapter names occurrence in its opening lines but has no section on it (NCERT page 90); the JEE Main 2027 and NEET (UG) 2026 syllabuses list it in Unit 11. Facts from beyond the NCERT books are labelled with their source.

Native metals and ores

• Minerals and ores. In the school usage, an ore mineral contains a metal that can be extracted economically. More precisely, mined ore can be a rock or mineral mixture; economic value depends on grade, processing and costs (NCERT Class 10 Science, Chapter 3, page 49). Whether a rock counts as ore is an economic question: the metal in it must be worth the cost of mining and processing (Wikipedia, “Ore”). Mined ore comes mixed with soil, sand and other impurities, called gangue (NCERT Class 10 Science, Chapter 3, page 50).
• Native transition metals. Small native grains of many metals are known, but only the platinum metals, gold, silver and copper are found uncombined in quantity (Wikipedia, “Native metal”). They are among the least reactive metals (NCERT Class 10 Science, Chapter 3, pages 49–50).
• Oxides, sulphides and carbonates. Most transition metals are reactive enough to be found only as compounds (reasoned from NCERT Class 10 Science, Chapter 3, page 50). For the textbook zinc route, sulphide and carbonate minerals are converted to oxides before reduction. This is not universal: other extraction routes can use sulphide melts, leaching or electrochemical steps. A sulphide is roasted, heated strongly in excess air; a carbonate is calcined, heated strongly in limited air (NCERT Class 10 Science, Chapter 3, page 51). For zinc, the last member of the 3d series:
  • 2ZnS + 3O₂ → 2ZnO + 2SO₂ (roasting)
  • ZnCO₃ → ZnO + CO₂ (calcination)

Common ores of iron, copper, chromium and manganese

• Iron. Most iron ore is iron oxide. Its chief minerals are magnetite and haematite, with goethite, limonite and the carbonate siderite (Wikipedia, “Iron ore”). From their formulas, pure magnetite is 72.4% iron by mass, haematite 69.9% and siderite 48.2% (Example 1 and Q8), the same figures as Wikipedia’s “Iron ore”. Magnetite holds both Fe²⁺ and Fe³⁺ and is drawn to a magnet (Wikipedia, “Magnetite”).
• Copper. Copper’s chief ore mineral is chalcopyrite, CuFeS₂, a brassy-yellow sulphide that holds iron as well as copper (Wikipedia, “Chalcopyrite”). Copper also occurs as the sulphide Cu₂S, which gives the metal on heating in air alone (NCERT Class 10 Science, Chapter 3, page 51). Among the oxidised copper ores are two carbonates, malachite and azurite (Wikipedia, “Copper extraction”); malachite, Cu₂CO₃(OH)₂, is green (Wikipedia, “Malachite”); the same atoms are often written CuCO₃·Cu(OH)₂ (reasoned).
• Chromium. In chromite, FeCr₂O₄, iron is +2 and chromium +3 (Wikipedia, “Chromite”), so it can also be written FeO·Cr₂O₃ (reasoned). NCERT gives the same formula, and makes chromates, and from them potassium dichromate, by fusing chromite ore with sodium or potassium carbonate in air (NCERT page 105).
• Manganese. Pyrolusite, mostly MnO₂, is a major manganese ore (Wikipedia, “Pyrolusite”; NCERT page 114 also gives it as MnO₂). Potassium permanganate is made by fusing MnO₂ with an alkali metal hydroxide and an oxidising agent such as KNO₃ (NCERT page 106), and NCERT’s Exercise 4.26 asks for the steps from pyrolusite ore to KMnO₄ (NCERT page 116).

Solved examples

Common mistakes to avoid

Quick revision summary

• Minerals occur naturally in the earth’s crust; ores are minerals from which a metal can be extracted profitably.
• Gold, silver, platinum and copper occur native; copper and silver also occur in sulphide and oxide ores.
• Many transition metals occur as oxides, sulphides or carbonates; in the textbook zinc route sulphides are roasted and carbonates calcined to oxides.
• Iron: magnetite, haematite, siderite; copper: chalcopyrite, Cu_₂S, malachite; chromium: chromite; manganese: pyrolusite.

Questions students ask

What is the most abundant transition metal in the earth’s crust?

Iron is the most abundant transition metal in the earth’s crust, about 5.63% of it by mass, and the fourth most abundant element after oxygen, silicon and aluminium (beyond the NCERT text; Wikipedia, “Abundance of elements in Earth’s crust”, from the CRC Handbook). The next transition metals are titanium, about 0.565%, and manganese, about 0.095%, so iron is about ten times as common as titanium (same source). Copper, for all its uses, makes up only about 60 parts per million of the crust (same source).

What is copper glance, and what is its formula?

Copper glance is an old name for chalcocite, copper(I) sulphide, Cu₂S, a dark, metallic-looking mineral and one of the richest copper ores (beyond the NCERT text; Wikipedia, “Chalcocite”). With Cu = 63.55 and S = 32.06 g mol^⁻¹ it is 127.10/159.16 × 100 = 79.9% copper by mass (reasoned), and heating it in air alone gives the metal (NCERT Class 10 Science, Chapter 3, page 51). Do not confuse it with chalcopyrite, CuFeS₂, the brass-yellow copper–iron sulphide that is the commonest copper ore mineral (Wikipedia, “Chalcopyrite”).

Is iron pyrites an ore of iron?

Iron pyrites, FeS₂, the brassy “fool’s gold”, is a common iron mineral but is not normally a principal iron-making ore: iron is made from the oxides magnetite and haematite, with goethite, limonite and the carbonate siderite (beyond the NCERT text; Wikipedia, “Iron ore”), while pyrite is used to make sulphur dioxide and sulphuric acid (Wikipedia, “Pyrite”). It also holds less iron than pure magnetite, haematite and siderite, 55.85/119.97 × 100 = 46.6% by mass (Fe = 55.85, S = 32.06 g mol^⁻¹), and its sulphur would first have to be roasted off as SO₂ (reasoned).

Is metallurgy in the JEE Main 2027 and NEET (UG) 2026 syllabus?

No, metallurgy, the extraction of metals from their ores, has no unit of its own in the JEE Main 2027 or the NEET (UG) 2026 syllabus, and the 2026–27 NCERT Class 12 Chemistry books have none either: their Units 1 to 10 run from Solutions to Biomolecules. Unit 11 of both syllabuses lists the transition elements’ “occurrence and characteristics”, and the only mention of extracting metals is in Unit 12, Coordination Compounds, which lists their importance “in qualitative analysis, extraction of metals and in biological systems” (see extraction of metals).

Practice questions

Try each question first, then open the answer to check your working.

1. Q1. Name the chief ores of chromium and manganese and give their formulas.

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   Chromium: chromite, FeCr₂O₄ (Wikipedia, “Chromite”; NCERT page 105). Manganese: pyrolusite, MnO₂ (Wikipedia, “Pyrolusite”; NCERT page 114).

2. Q2. Name three transition metals found in the free state, and say why they are found that way.

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   Gold, silver and platinum (copper too). They are among the least reactive metals, at the bottom of the activity series, so they are often found uncombined (NCERT Class 10 Science, Chapter 3, pages 49–50).

3. Q3. What is the difference between a mineral and an ore?

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   NCERT uses mineral for a naturally occurring elemental or compound form of a metal. In geology a mineral is a naturally occurring solid with an ordered structure and characteristic composition; an ore is economically workable mineral-bearing material (NCERT Class 10 Science, Chapter 3, page 49).