1900 is a common date for gold sovereigns from Great Britain. Sovereigns contain 0.2354 troy ounces of gold, so you can figure the value from that (see below). Your coin is worth its weight in gold, plus a little extra for being a nice piece of art.
A half sovereign looks the same as your sovereign, only smaller and less gold. Here are the stats. Measure the diameter of your coin to find out which you have:
HALF SOVEREIGN: 19 mm diameter, 0.1177 troy ounces gold
SOVEREIGN: 23 mm diameter, 0.2354 troy ounces gold.
Referring to kitco.com, an ounce of gold is worth $1340 US Dollars right now, so 0.235 times $1340 gives $315 as the base value of a sovereign, $157 as the base value of a half sovereign. Check kitco today. The price changes daily.
In average circulated condition collectors might pay about $30 more than this. For a fully uncirculated coin authenticated and mounted in a numismatic holder, the addition of value might reach $100 or $150 more than the base gold value. Dealers would pay $50 to $150 less if they were buying the coin from you.
For sovereigns and half sovereigns between 1893 and 1901, the specific date of the coin does not matter. The values above apply to all dates.
Check closely. You might have a sovereign or half sovereign from Australia. The S=Sydney, M=Melbourne, and P=Perth mint marks are found above the date. They are sometimes very difficult to see. If you have an Australian coin, click to this CoinQuest link.
Quite often sovereigns are used for jewelry. If this is the case, the value reverts to basic gold value, as all numismatic (coin collector) value disappears.