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 "Small Date" variety features a smaller date with noticeably smaller numbers. All coins of this variety feature a Plain "4" in the 1842 date with a straight horizontal end on the right side of the "4". The other variety is known as the "Large Date" with larger numbers - and all coins of this variety have a Crosslet "4" which features a small vertical line through the right-side end of the "4". 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