Which of the following is the main composition of granite?
💎 Understanding Granite's Composition
Granite is an intrusive igneous rock, which means it forms from the slow cooling of magma deep within the Earth's crust. This slow cooling allows large, visible crystals of different minerals to form. The specific combination of these minerals gives granite its characteristic appearance and properties.
🔬 Detailed Analysis of the Options
A. Quartz, feldspar and mica
This is the correct answer. These three minerals are the essential components that define granite.
- Quartz: Typically makes up 20-60% of granite. It is a very hard mineral that gives granite its durability. It usually appears as glassy, greyish, or semi-transparent grains.
- Feldspar: This is the most abundant mineral in granite. It gives granite its primary color, which can be pink, white, grey, or reddish.
- Mica: Present in smaller amounts, mica appears as shiny black or silvery specks (the two main types are black biotite and silvery muscovite). It adds sparkle to the rock.
B. Quartz, and lime
This is incorrect. Lime (calcium carbonate) is the primary constituent of sedimentary rocks like limestone and its metamorphic form, marble. It is not a main component of granite.
C. Quartz, and silica
This option is redundant and incomplete. Quartz is a form of silica (silicon dioxide, SiO₂). So, this is like saying "apples and fruit." While granite is rich in silica, this option fails to mention the other essential minerals like feldspar and mica that are required for a rock to be classified as granite.
D. Silica, lime and alumina
This is incorrect. While granite's minerals (feldspar and mica) are silicates containing silica and alumina, this list wrongly includes lime. This combination of ingredients is more characteristic of the raw materials used to make cement, not the mineral composition of granite.
📊 Summary: Main Components of Granite
| Mineral | Typical % in Granite | Appearance / Role |
|---|---|---|
| Quartz | 20 - 60% | Hard, durable; glassy grey grains. |
| Feldspar | Up to 65% | Gives primary color (pink, white, grey). |
| Mica | 5 - 10% | Shiny black/silvery specks. |
💡 Study Tips
- Look at a Countertop: The next time you see a granite countertop, try to identify the three main components: the glassy grey (Quartz), the main colored parts (Feldspar), and the little black or silver sparkles (Mica).
- QFM - Quality For Masonry: Use the acronym QFM (Quartz, Feldspar, Mica) to remember the three essential minerals.
- Lime is for Limestone: Always associate lime with limestone and marble, not with igneous rocks like granite.