Why are shellfish population often a good indicator of water quality

The number of shellfish in a body of water determines its quality due to how shellfish require a high quality of water to survive. Therefore, the relationship between the quality of water and the number of shellfish are directly proportional. The more shellfish there are, the better the quality of water. 

Characteristic expected of mineral from lava at earth's surface

phaneritic textures in which phaner means visible so phaneritic textures are standard of impertinent volcanic rocks. these rocks crystallized gradually under the surface of earth. when the magma cools deliberately then the ores have chance to develop and produce long crystals.