Flowers, rivers, and rock share this word.

I hang from a roof and look like a sharp spike, I’m made of water, not a pike also I melt when it’s sunny and freeze when it’s cold.

Rainbow be my nature though I favor gray and green Precious be my value though I'm far from most obscene Silica hydrated will diffract and sparkle light Truly rather useless 'cept adornment's lovely sight

The fifth of five, I'm Japanese, the hardest to describe From seaweed succulent to beef and cheese, I am ascribed

I have been a form of currency I’m essential for life, but too much of me can lead to death