Here’s how Facebook paid for Instagram (and how much it’ll still pay if the deal doesn’t work out)

Facebook has just filed an amended S1 form with the SEC, and in it, we learn just how the social network’s acquisition deal with Instagram went down. We’ve also learned how much of the $1 billion price tag was split between cash and company stock.

The filing reveals Facebook paid 23 million shares of Facebook common stock as well as $300 million in cash to acquire mobile photo-sharing app Instagram. Also, Facebook will pay out a $200 million breakup fee if regulators don’t green-light the acquisition.

Just days before the $1 billion deal, Instagram took a round of funding valuing it at around $500 million.

According to today’s S1 update, the deal is expected to fully close within the second quarter of 2012.

“Following the closing of this acquisition, we plan to maintain Instagram’s products as independent mobile applications to enhance our photos product offerings and to enable users to increase their levels of mobile engagement and photo sharing,” the filing reads.

“We believe that mobile usage of Facebook is critical to maintaining user growth and engagement over the long-term, and we are actively seeking to grow mobile usage, although such usage does not currently directly generate any meaningful revenue.”

In the filing, Facebook admits that large-scale acquisitions such as the Instagram deal are still fairly uncharted territory, and future acquisitions of similar scope might “require significant management attention, disrupt our business, result in dilution to our stockholders, and adversely affect our financial results… Our ability to acquire and integrate larger or more complex companies, products, or technologies in a successful manner is unproven.”

The SEC filing today still contains no details on where Facebook’s stock price will start, and it names no date for the IPO to take place. Stay tuned for those details over the next couple weeks.