Problem 163 - A Complete Resource Book in Chemistry for JEE Main

Question

Among the following minerals, siderite, malachite, cerussite, anglessite, smithsonite, diaspore, mica and corundum, the number of carbonate minerals is

Step-by-Step Solution

Answer

The number of carbonate minerals is 4.

Step 1: Identify Carbonate Minerals

Carbonate minerals contain the carbonate ion \( \text{CO}_3^{2-} \). Review each given mineral to check if it belongs to the carbonate group. The minerals listed are: siderite, malachite, cerussite, anglesite, smithsonite, diaspore, mica, and corundum.

Step 2: Classify Each Mineral

- **Siderite**: \( \text{FeCO}_3 \), contains carbonate. - **Malachite**: \( \text{Cu}_2(\text{OH})_2\text{CO}_3 \), contains carbonate.- **Cerussite**: \( \text{PbCO}_3 \), contains carbonate.- **Anglesite**: \( \text{PbSO}_4 \), a sulfate mineral, does not contain carbonate.- **Smithsonite**: \( \text{ZnCO}_3 \), contains carbonate.- **Diaspore**: \( \text{AlO(OH)} \), a hydroxide mineral, does not contain carbonate.- **Mica**: A silicate mineral, does not contain carbonate.- **Corundum**: \( \text{Al}_2\text{O}_3 \), an oxide mineral, does not contain carbonate.

Step 3: Count Carbonate Minerals

Tally the number of minerals that contain the carbonate ion. Based on the classification: siderite, malachite, cerussite, and smithsonite are carbonate minerals.

Key Concepts

Siderite

Siderite is a fascinating mineral that belongs to the group of carbonate minerals. It is known for its chemical formula, \( \text{FeCO}_3 \), which means it contains iron (Fe) and the carbonate ion \( \text{CO}_3^{2-} \). This mineral typically forms in sedimentary and hydrothermal environments, often found with minerals like chert or hematite.

Siderite is typically brown or reddish-brown in color and is sometimes mistaken for similar minerals like brown iron ore. One of its distinctive features is its property to alter and weather to lepidocrocite, another iron mineral, over time.

Understanding siderite is crucial since it not only enriches the study of carbonate minerals but also aids geological processes and can be an indicator of the past environment where it formed.

Mineral Classification

The classification of minerals is a way of organizing the vast variety of minerals found on Earth. This classification helps in identifying minerals efficiently, based on specific criteria, and is essential for geologists and mineralogists in their studies.

Minerals are generally classified by their chemistry or crystal structure. The most common broad categories include:

• Silicates: The most abundant mineral group. Examples include mica and feldspar.
• Carbonates: Defined by the presence of the carbonate ion \( \text{CO}_3^{2-} \), such as siderite, cerussite, and smithsonite.
• Oxides: Composed mainly of metal elements combined with oxygen, like corundum.
• Sulfates: Contain the sulfate ion \( \text{SO}_4^{2-} \); anglesite is an example.
• Halides, sulfides, phosphates, and hydroxides: Other categories based on different combinations of elements.

Sorting minerals into these categories allows for systematic study and helps predict properties and uses.

Carbonate Ion

The carbonate ion, \( \text{CO}_3^{2-} \), is the fundamental building block of carbonate minerals. It is a polyatomic ion composed of one carbon atom centrally bonded to three oxygen atoms, forming a triangular planar structure.

The charge of \( -2 \) results from the two extra electrons that provide the ion its negative charge. Due to this charge, carbonate ions can easily bond with positively charged metal ions to form various carbonate minerals, like calcium carbonate (limestone) or iron carbonate (siderite).

Understanding the carbonate ion is key in geology, not only for identifying minerals but also for environmental science, as carbonate ions play a crucial role in the carbon cycle and in maintaining oceanic pH levels.

Chemical Formula

The chemical formula of a mineral is a symbolic representation that provides insight into its composition and structure. For instance, siderite's formula \( \text{FeCO}_3 \) informs us that it is made of iron, carbon, and oxygen and belongs to carbonate minerals.

Writing and interpreting chemical formulas:

• Know each element: Each symbol in the formula represents a chemical element.
• Subscripts: These show how many atoms of each element are present. If no subscript is present, it implies one atom.
• Charge: Often, chemical formulas include notations on ionic charge, especially for complex ions like carbonate \( \text{CO}_3^{2-} \).

Chemical formulas are more than just numbers and letters. They reveal essential details about a mineral's formation and properties, aiding in the study and classification of minerals.