I imagine what I am going to say will be perceived as offensive, but the question OP posed was about what the rock was made of, not how Smith used it. Secondly, there will be a preponderance of comments in this thread sharing or stating uncited "facts" about Joseph Smith, Mormons, and Mormonism which will be interesting, controversial or considered informative, especially to those unfamiliar with the subject matter, but at their root would be unfair to those interested in actual scholarly or reasoned discussion about the stone or Smith and his adherents. So, in the interest of fairness, before one asks if Smith was a con man or a fraud, consider the original intent of the conversation. I scanned through the thread and saw people saying things like "Most Mormons don't know this or that" or "the LDS Church deliberately sought to deceive or cover this or that up", etc. I imagine some of those comments will come from former or disaffected adherents, which while that lends some veracity, without, for instance citing a credible source of a study that shows "most Mormon respondents said ..." then its purely anecdotal or speculative. That is the kind of thing that I think does not contribute in a meaningful way to the conversation, especially in a thread about the geologic origins of a rock.

But, alas, I know I am spitting in the wind. It's just when people who aren't particularly fond of Mormonism are allowed to control the conversation about it, I find it a little unfair, and as a geek who loves to read what actual scientists think about sacred objects I care about, that's something to consider. Hopefully there will be more balance, but I know from my own experience when it comes to discussion of Mormonism on Reddit, that the conversation tends to sway towards disdain for Mormons and Mormonism, its origins, founder, etc. And yes, I am a Mormon.