The black fine sand is a dark secondary mineral "glauconite" formed in the specific marine environment. After millions of years of washout by Pacific waves, the glauconite is affected by the current and transported to the nearshore, then pushed to the shore by the waves to form a beach. Not the whole beach is black sand, there is a really black area, ten years ago, the summer vacation came to see the sunset super bar. It's winter this time.