What this coin looks like (obverse, reverse, mint mark location, special features, etc.):
There were two major varieties and styles of the 1842 $10 Gold Liberty Head Eagle. This "Large Date" variety features a larger date with noticeably larger numbers. All coins of this variety feature a Crosslet "4" in the 1842 date with a vertical line struck through a straight horizontal end on the right side of the "4". The other variety is known as the "Small Date" with smaller numbers - and all coins of this variety have a Plain "4" which features a plain straight horizontal end on the right side of the 4 with no vertical crosslet. The difference between the Small Date vs Large Date (and Plain 4 vs Crosslet 4) is depicted below in the example comparison image (Source of example images is courtesy of Heritage Auction Galleries):
Coin valuation chart: Typical coin prices, values and worth per grade or condition - in USD