These are amazing coins: old guinea coinage from King William (Gulielmus) III. And they are worth a bundle.
1/2 GUINEA: 21 mm diameter, 0.123 troy ounces gold
1 GUINEA: 25 mm diameter, 0.246 troy ounces gold
5 GUINEAS: 36 mm diameter, 1.231 troy ounces gold
Being so old and valuable, catalog values do not mean much. Each coin stands on its own merits of luster, strike, wear, and eye appeal. Damaged coins (scratches, stains, gouges, cleanings) are still valuable, although much less than undamaged material. Use the catalog values below as approximate guides only. The dates on these coins do not affect value strongly, although the older dates in the 1690s usually fetch a little more than the 1701-dated coins.
worn: $400 US dollars approximate catalog value
average circulated: $1200
well preserved: $3500
fully uncirculated: $7000
worn: $600 US dollars approximate catalog value
average circulated: $3800
well preserved: $6500
fully uncirculated: $11000
worn: $2500 US dollars approximate catalog value
average circulated: $5000
well preserved: $14000
fully uncirculated: $24000
The coin in our picture comes from Noble Numismatics, and CoinQuest thanks them for use of their coin photo.