No web site can give you the value of any object, sight-unseen.
Take your pendant to a jeweler, or to a pawn shop and ask for a valuation.
Modified coins have no collector value. Any value the pendant may have would be as a piece of jewellery. The coin itself might get up to £2 GBP if it was in mint condition and had not been silver plated.
The Sterling Silver Guardian Angel Wing Pendant is an excellent gift for any mother, and is sure to have sentimental value for years to come.
You can find a high-quality silver chain necklace for a pendant at jewelry stores, online retailers like Amazon or Etsy, or specialty shops that sell fine jewelry. Look for chains made of sterling silver or higher grades of silver for better quality.
A silver pendant could be a pure substance, but if it is a modern commercially produced pendant, it is more likely to be a mixture, because pure silver is so soft that it is very easily damaged. The most nearly pure silver alloy commonly used in jewelry is called "sterling silver" and contains 92.5 % silver.
Your medallion is one (1) troy ounce of sterling silver (.925) which has an intrinsic value of about $30 right now.
Below is a link to find the value of silver per ounce.
The "gk" on a silver pendant typically stands for the initials of the designer or manufacturer. It can also denote a specific hallmark or brand associated with silver jewelry. To determine its exact meaning, it's helpful to research the context in which the pendant was made or consult with a jeweler.
A gold pendant should be worn with a gold necklace. If the pendant has mostly white or another color in it and just a small amount of gold it might look alright with a silver necklace. Try the gold pendant with the silver necklace and see how it looks, if you think it looks good than by all means wear it.
Modified coins have no collector value. Any value would be associated with the pendant.
The "925" on a pendant indicates that the metal is made of sterling silver, which consists of 92.5% silver and 7.5% other metals, typically copper. "AMG" may refer to a specific brand, designer, or manufacturer associated with the pendant. Together, the markings suggest that the pendant is made of high-quality sterling silver, potentially from a reputable source.
an ivory pendant with a ship an a eoman waving goodbye to someone
The Silver Pendant in the game Dark Souls can deflect dark sorcery for about three seconds. While this isn't a very long amount of time, the number of times the pendant can be used is unrestricted.