Occurrence of Metals in Nature
Forms, factors and examples of different types of metals
Introduction
Metals are elements that generally have good electrical and thermal conductivity, malleability, ductility, and high melting points. While metals make up about 75% of all known elements, they are rarely found in their pure form in nature. This blog post explores how and where metals occur in the Earth’s crust and what forms they take in nature.
Exam Key Point:
The Earth’s crust contains approximately 25% metals by mass, but most metals exist in combined states as minerals and ores rather than in their pure elemental form.
Forms of Metal Occurrence in Nature
Native State
Metals found in their free or uncombined state in nature.
Examples:
- Gold (Au)
- Silver (Ag)
- Platinum (Pt)
- Copper (Cu) – sometimes
Combined State as Minerals
Metals found in combined form with other elements as minerals.
Common Forms:
- Oxides (metal + oxygen)
- Sulfides (metal + sulfur)
- Carbonates (metal + CO₃²⁻)
- Halides (metal + halogen)
Ores
Minerals from which metals can be extracted profitably and economically.
Not all minerals are ores, but all ores are minerals. An ore contains a sufficient concentration of metal to make extraction economically viable.
Common Metal Ores and Their Composition
| Metal | Ore Name | Chemical Formula | Type of Ore |
|---|---|---|---|
| Iron (Fe) | Hematite | Fe₂O₃ | Oxide |
| Iron (Fe) | Magnetite | Fe₃O₄ | Oxide |
| Aluminum (Al) | Bauxite | Al₂O₃·2H₂O | Hydrated Oxide |
| Copper (Cu) | Copper Pyrites | CuFeS₂ | Sulfide |
| Copper (Cu) | Malachite | CuCO₃·Cu(OH)₂ | Carbonate |
| Zinc (Zn) | Zinc Blende | ZnS | Sulfide |
| Lead (Pb) | Galena | PbS | Sulfide |
| Tin (Sn) | Cassiterite | SnO₂ | Oxide |
| Mercury (Hg) | Cinnabar | HgS | Sulfide |
| Magnesium (Mg) | Dolomite | MgCO₃·CaCO₃ | Carbonate |
| Sodium (Na) | Rock Salt | NaCl | Halide |
Exam Key Point:
Memorize the chemical formulas and types of the most common ores, especially for iron, aluminum, copper, and zinc, as these are frequently asked in examinations.
Distribution of Metals in Earth’s Crust
The Earth’s crust contains a variety of metals, but they are not evenly distributed. Some metals are abundant, while others are quite rare. The abundance of metals in the Earth’s crust is influenced by their chemical properties and geological processes.
Abundant Metals
- Aluminum (Al) – 8.1% of Earth’s crust
- Iron (Fe) – 5.0% of Earth’s crust
- Calcium (Ca) – 3.6% of Earth’s crust
- Sodium (Na) – 2.8% of Earth’s crust
- Potassium (K) – 2.6% of Earth’s crust
- Magnesium (Mg) – 2.1% of Earth’s crust
Less Abundant Metals
- Titanium (Ti) – 0.44% of Earth’s crust
- Manganese (Mn) – 0.09% of Earth’s crust
- Copper (Cu) – 0.006% of Earth’s crust
- Zinc (Zn) – 0.007% of Earth’s crust
- Lead (Pb) – 0.0014% of Earth’s crust
- Silver (Ag) – 0.000008% of Earth’s crust
- Gold (Au) – 0.0000004% of Earth’s crust
Exam Key Point:
Aluminum is the most abundant metal in the Earth’s crust, followed by iron. Precious metals like gold and silver are among the rarest. The relative abundance helps explain why some metals are more expensive than others.
Factors Affecting Metal Distribution
Geological Factors
- Plate Tectonics – Movement of Earth’s crust creates zones where metals concentrate
- Volcanic Activity – Brings minerals from deep inside Earth to the surface
- Sedimentation – Formation of layers containing metal deposits
- Weathering – Chemical breakdown of rocks, concentrating certain metals
Chemical Factors
- Reactivity – More reactive metals are less likely to be found in native state
- Affinity – Tendency of certain metals to bind with specific elements
- Solubility – Affects how metals are transported and deposited
- Oxidation State – Determines stability of metals in different environments
Exam Key Point:
The reactivity of a metal largely determines its form of occurrence. Less reactive metals (Au, Pt, Ag) are often found in native state, while more reactive metals (Na, K, Al) are always found in combined states.
Occurrence Patterns Based on Reactivity
Highly Reactive Metals
Examples: Potassium (K), Sodium (Na), Calcium (Ca), Magnesium (Mg), Aluminum (Al)
Occurrence: Always found in combined state, never as free elements
Common Forms: Oxides, carbonates, silicates, halides
Moderately Reactive Metals
Examples: Zinc (Zn), Iron (Fe), Lead (Pb), Copper (Cu)
Occurrence: Usually found as oxides, sulfides, or carbonates
Common Forms: Fe₂O₃, ZnS, PbS, CuFeS₂
Least Reactive Metals
Examples: Gold (Au), Silver (Ag), Platinum (Pt)
Occurrence: Often found in native (free) state
Common Forms: Pure metal nuggets or deposits
Exam Application:
If asked to predict how a particular metal might occur in nature, consider its position in the reactivity series:
- Metals above hydrogen always occur in combined form
- Metals far below hydrogen (Au, Pt) typically occur in native state
- Metals like copper may occur both in native state and as compounds
Major Metal Deposits Around the World
Understanding the geographic distribution of major metal deposits helps in appreciating the global nature of metal resources and international trade.
Iron
- Australia – Pilbara region
- Brazil – Carajás Mine
- China – Provinces of Liaoning and Sichuan
- Russia – Kursk Magnetic Anomaly
- India – Odisha, Jharkhand
Aluminum (Bauxite)
- Australia – Weipa, Gove
- Guinea – Boké
- Jamaica
- Brazil – Amazon region
- China – Provinces of Shanxi and Henan
Copper
- Chile – Escondida Mine
- Peru – Antamina Mine
- USA – Bingham Canyon, Utah
- Indonesia – Grasberg Mine
- Zambia – Copper Belt
Gold
- South Africa – Witwatersrand Basin
- USA – Nevada
- Australia – Kalgoorlie
- Russia – Siberia
- Canada – Yukon
Exam Key Point:
For exams, focus on understanding which countries are the leading producers of major metals and what forms those metals are typically found in. Also note that the concentration of ores varies widely across deposits, affecting their economic viability.
Exam Practice Questions
Question 1:
Which of the following metals is most likely to be found in its native state in nature?
- Sodium
- Iron
- Gold
- Aluminum
Answer: c) Gold
Explanation: Gold is one of the least reactive metals and therefore can exist in its native (free) state in nature without combining with other elements.
Question 2:
Bauxite is the principal ore of which metal?
- Iron
- Copper
- Zinc
- Aluminum
Answer: d) Aluminum
Explanation: Bauxite, primarily composed of aluminum hydroxide minerals, is the main ore from which aluminum is extracted industrially.
Question 3:
Which of the following is NOT a factor affecting the occurrence of metals in Earth’s crust?
- Reactivity of the metal
- Geological processes like plate tectonics
- The metal’s position in the periodic table
- The metal’s commercial value
Answer: d) The metal’s commercial value
Explanation: The commercial value of a metal is a human-assigned attribute and does not affect how the metal naturally occurs in Earth’s crust. The other factors are all scientific determinants of metal occurrence.
Summary
• Metals occur in nature in different forms depending primarily on their reactivity.
• Very reactive metals (K, Na, Ca, Mg, Al) are always found in combined states as compounds.
• Moderately reactive metals (Zn, Fe, Pb) are usually found as oxides, sulfides, or carbonates.
• Less reactive metals (Cu, Hg) may be found in both free and combined states.
• Least reactive metals (Au, Pt, Ag) are often found in their native state.
• An ore is a mineral from which a metal can be profitably extracted. Not all minerals containing metals are ores.
• The distribution of metals in Earth’s crust depends on geological processes, chemical properties of metals, and environmental conditions during formation.
• Understanding the patterns of metal occurrence helps in developing extraction strategies and identifying potential mining sites.
