Starbucks is ramping up its tea business with a $620 million purchase of Atlanta-based tea seller Teavana.

The coffee giant said Wednesday that it sees a growing market for tea. Starbucks already owns the Tazo tea brand.

Starbucks plans to expand Teavana Holdings Inc.'s network of 300 mall-based stores and add stores outside of malls too.

Teavana shareholders will receive $15.50 per share in cash in the deal, which is expected to close by the end of the year.

Teavana gained more than 50 percent, to $15.45, in afternoon trading. Starbucks Corp. shares slipped 2 percent.