Natural resources could be the answer
Color and luster are two ways to identify an unknown metal. Other ways include weight and composition.
Only three Caribbean countries have oil and natural gas reserves: Barbados, Cuba, and Trinidad and Tobago. Of these, Trinidad and Tobago is the only significant exporter. *Source: Oil and Gas Journal, December 23, 2002. Trinidad and Tobago is the Caribbean's largest producer of oil and gas.