Square Inc. Chief Executive Officer Jack Dorsey said on Friday the fintech firm is looking to build a bitcoin mining system based on custom silicon and open source for individuals as well as businesses. This would add to Square’s existing bitcoin-focused projects including a business to build an open developer platform, as well as a hardware wallet for the cryptocurrency. “If we do this, we’d follow our hardware wallet model: build in the open in collaboration with the community,” Dorsey said on Twitter. A team led by Square’s hardware lead, Jesse Dorogusker, will investigate requisites for Square to take on the project to build a bitcoin mining system. In his Twitter thread, Dorsey also said that silicon design or chip design is too concentrated in a few companies, leading to supply constraints. Shares of Square were up about 1 percent in extended trading. On Friday, bitcoin topped $60,000 for the …