India is one of the largest centres for polishing diamonds and gems and manufacturing jewellery; it is also one of the two largest consumers of gold. After crude oil and petroleum products, the export and import of gold, precious metals, precious stones, gems and jewellery accounts for the largest portion of India's global trade. The industry contributes about 7% of India's GDP, employs millions, and is a major source of its foreign-exchange earnings. The gems and jewellery industry, in 2013, created ₹251,000 crore (US$35 billion) in economic output on value-added basis. It is growing sector of Indian economy, and A.T. Kearney projects it to grow to ₹500,000 crore (US$70 billion) by 2018.
For a person working for a wage, their source of income is their job, or their labor (aka their time that they sell to someone). But you can own a house, and rent it out, and when your renters pay you renter every month, the source of that income check is your rental property, or your house. It would just be called rental income. If you have money in the bank in an account that pays interest, those interest payments are another source of income. We can say the source is interest payments, or we can identify the asset that is generating rent, and say your money in the bank that is generating “rent” (aka interest) is your source of income.