What is this solid made of?

There are sediments at the bottom of this lake that have accumulated over centuries.

My mother carefully keeps the brush made with my fetal hair as a birth commemoration.

His art style is unique, it's neither fish nor fowl.

He tried to solve the problem all day long.

Our store has a regular day off every Monday.

Our project is scheduled to be completed on the twentieth day of the month.

Day after day, he continued to strive to solve the problem.

His poem depicts a world of nothingness.

Today is my birthday, a very lucky day.