The Black Mermaid

The Black Mermaid by Shikhar Dixit (a Short Story Contest entry) 

Her origins are lost in the mists of time. Shadows of rumors place her far back in ancient Mesopotamia. A Muslim cleric living in the shadow of Turkey's Mount Nemrut claims she was discovered by nomadic Homo Ergaster upon African savannahs.

Physicists speculate on the black substance, resistant to any and all methods of modern forensic inquiry, including the powerful Zetawatt-Equivalent Ultrashort Pulse Laser.

Her very presence induces horrific nightmares.