Can any Stone Float on Water?

YES. Pumice is the only kind of stone that floats on water before sinking. It is a lightcoloured volcanic rock.

When a volcano erupts, the hot lava comes into contact with the cooler air. The lava cools down and solidifies almost immediately. Secondly, as the pressure rapidly decreases, gas bubbles are created in the rock before it hardens. As a result, the pumice gets its characteristic hard, vesicular (full of cavities) spongy appearance.

Pumice has an average porosity of 90 per cent and is less dense than water. As long as its bubbles are filled with air, it floats. When water enters the pores, the stone becomes heavy and sinks.

It is not uncommon to find floating masses of pumice near volcanic islands in the ocean. In August 2006, the crew of the Maiken, a yacht sailing in the South Pacific near Tonga, encountered a wide belt of densely packed pumice, just after a submarine volcano Home Reef had erupted. The pumice resembled a blanket of sand on water!

Pumice is used in the manufacture of lowweight concrete blocks and stone-washed jeans. Pumice stones are used in pedicure in beauty salons.

TRUE OR FALSE?

The skin of bananas kept in the refrigerator turn black because the fruit becomes rotten.

False. The outer skin of the banana darkens due to a process called oxidation. Banana peels are rich in phenolic acids, which play an important role in the defense mechanism of plants. Below 100C, the phenolic acids oxidize to form quinones which turn the peel black. This is known as ‘chilling injury’. But the inner fruit remains white and fresh as the cold inhibits the release of ethylene gas which stimulates ripening.