Problem 72 - A Complete Resource Book in Chemistry for JEE Main

Question

The important ore of zinc is (a) cryolite (b) calamine (c) malachite (d) gibbsite

Step-by-Step Solution

Answer

Calamine (b) is the important ore of zinc.

Step 1: Identify the Question

Read the question carefully to understand which mineral is an important ore of zinc. The options provided are cryolite, calamine, malachite, and gibbsite.

Step 2: Understand the Options

Analyze each of the given options: (a) cryolite, (b) calamine, (c) malachite, and (d) gibbsite. Each option represents a specific mineral, only one of which is associated with zinc ore.

Step 3: Recall Knowledge on Zinc Ores

Remember that calamine is a well-known ore of zinc. It primarily contains zinc carbonate (ZnCO₃) or zinc silicate, both of which are important sources of zinc.

Step 4: Eliminate Incorrect Options

Identify that cryolite (a) is an ore used primarily for aluminum, malachite (c) is a copper ore, and gibbsite (d) is an aluminum ore, not zinc. This leaves calamine (b) as the correct answer.

Step 5: Select the Correct Option

Based on the analysis, choose calamine (b) as the most important ore of zinc from the given options.

Key Concepts

Calamine

Calamine is an important ore of zinc and plays a critical role in the extraction process of this essential metal. Primarily, calamine is not a unique mineral. Instead, it is a name once commonly used to refer to two distinct zinc minerals: zinc carbonate (ZnCO₃) and zinc silicate.

These minerals are pivotal in the zinc extraction industry as they are among the vital sources of zinc metal. Historically, when miners referred to calamine, they didn't distinguish between these two forms; however, modern mineralogy differentiates them simply as Smithsonite for zinc carbonate and Hemimorphite for zinc silicate. This clarification is important for mineralogical studies.

• Calamine as a term is less favored in modern mineralogy.
• It encompasses both zinc carbonate and zinc silicate.
• This ore has been traditionally significant in zinc mining and refining.

Zinc Carbonate

Zinc carbonate, chemically known as ZnCO₃, is commonly identified in its mineral form as Smithsonite. This mineral is one of the key ores of zinc and was historically called calamine along with zinc silicate. Smithsonite occurs in various shades from white to a beautiful green due to the presence of other impurities.

This mineral forms as a secondary mineral in zinc-rich deposits through the weathering of other more primary ore minerals. Its formation through natural processes makes it a noteworthy source for the mining of zinc, which is used in various applications.

• It is used in zinc metal production.
• Zinc from Smithsonite has applications in alloys, galvanization, and die-casting.
• Its secondary nature makes it a significant indicator of underlying zinc deposits.

Zinc Silicate

Zinc silicate, often referred to as Hemimorphite, is another critical ore of zinc, formerly grouped under the broad term "calamine." This mineral is defined by its chemical formulation, Zn₄Si₂O₇(OH)₂·H₂O, distinguishing it from zinc carbonate.

Hemimorphite occurs in the oxidized zones of zinc deposits, where it results from the alteration of primary zinc minerals. It often presents in vibrant blue or green crystals, making it attractive both for industrial zinc extraction and as a sought-after specimen for collectors.

• Important in the historical context of zinc extraction.
• The presence of Hemimorphite in deposits can point to richer sources of zinc.
• In addition to its industrial uses, its aesthetic appearance gives it value in gemstone markets.