Utilize the input text as a context reference, choose the right relationship between Petra Diamonds and diamond from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

Petra Diamonds (LSE: PDL.L - news ) declined after saying full-year revenues dropped 10% to $425m on the back of lower diamond prices, as expected.

Answer: industry