Answer:
To allow the proper amount of water to be passed through to other communities.
Explanation:
When magma<span> cools, </span>crystals<span> form because the solution is super-saturated with respect to some </span>minerals<span>. If the </span>magma<span> cools quickly, the </span>crystals<span> do not have much time to form, so they are very small. If the </span>magma<span> cools slowly, then the </span>crystals<span> have enough time to grow and become large.</span>
The quartz is more resistant to abrasion and chemically more resistant than the feldspar. The result is that the quartz remains in the stream but the feldspar breaks down to clay or is dissolved.
(this is from coursehero.com)
