Q1.
Have you visited a place where large crystal deposits can be observed in nature?
Answer
Natural crystals grow wherever a mineral-rich solution is left undisturbed for a very long time — in caves, in mines and inside the Earth’s crust.
Sample answer: On a school trip to Sohra (Cherrapunji) in Meghalaya we went into the Mawsmai Cave (Fig. 5.10a). Water dripping through the limestone roof carries dissolved calcium compounds. As each drop hangs at the roof and slowly loses water and carbon dioxide, the solution becomes saturated and a little solid is deposited. Over thousands of years these deposits build up into stalactites hanging down and stalagmites rising from the floor. Quartz (Fig. 5.10b), with its clear six-sided pointed crystals, is another beautiful example found in mines and rock cavities.
Why nature makes better crystals than we do: The size of a crystal depends on how slowly it grows. In the laboratory we cool a solution over an hour; in a cave the solution is fed drop by drop over centuries. Extremely slow growth means very few nuclei and unlimited time for each to add particles in a perfectly regular geometric pattern — which is why natural crystals can be enormous and beautifully formed.
Try this: If you cannot visit a cave, look at rock salt (sendha namak), mishri, alum or quartz from a local shop under a magnifying glass. Sketch the shape you see — each compound has its own characteristic crystal shape.