Silicon is an important constituent of:

Options

A. Rocks
B. Amalgams
C. Chlorophyll
D. Haemoglobin

Explanation

To solve the question "Silicon is an important constituent of:", we will analyze each option provided.

### Step-by-Step Solution:

1. **Identify the Element**: Silicon (Si) is a chemical element with the atomic number 14. It belongs to the carbon family and is known for its role in various compounds.

2. **Evaluate the Options**: We need to determine which of the given options silicon is a significant component of.

- **Option A: Rocks**: Silicon is a major component of rocks, primarily in the form of silica (SiO2). Silica is a common mineral found in many types of rocks, including granite and sandstone.

- **Option B: Amalgams**: Amalgams are alloys that primarily consist of mercury (Hg) and are used in dental fillings. Silicon is not a constituent of amalgams.

- **Option C: Chlorophyll**: Chlorophyll is the green pigment found in plants, which is essential for photosynthesis. It contains magnesium (Mg) but does not contain silicon.

- **Option D: Hemoglobin**: Hemoglobin is a protein in red blood cells that carries oxygen. It contains iron (Fe) but does not contain silicon.

3. **Conclusion**: After analyzing all the options, we find that silicon is indeed an important constituent of rocks, specifically in the form of silica (SiO2). Therefore, the correct answer is:

**Option A: Rocks.**