What you have is refered to as a Silver Strike... Most of the machines have been removed from all the hotels except for a few downtown in Las Vegas and other places in the US.
You have to be careful when you buy them because folks think they are pure silver or contain one ounce and they do not!
There is a club that focuses on collecting theses:
http://www.silverstrikers.com/Strike Composition
$2 and $3 strikes are made of Brass.
$7 strikes are .999 Silver with approximate weight of 0.65 troy ounces.
$10 strikes have a .999 Silver center insert, outer ring is Brass (additional info here), approximate Silver weight is 0.60 troy ounces of Silver. Sometime in 2005, a new thinner center insert strikes with less silver (~ 0.50) appeared. In 2009 CLAD (no .999) $10 strikes appeared, even some red capsules. However, the red capsules should return to .999 silver.
$20 strikes have a .999 Silver outer ring with some 24kt Heavy Electroplating (HE) and a Bronze 24kt Heavy Gold Electroplate (HGE) on the center insert, approximate Silver weight is 0.75 troy ounces of Silver.
$28 strikes are .999 Silver with 24kt Gold Plating (GP), approximate Silver weight is 0.65 troy ounces.
$40 strikes are .999 Silver with 24K Heavy Electroplate (HE), approximate Silver weight is 1.54 troy ounces for the large size $40 strikes and 1.26 troy ounces for the small size $40 strikes.
$200 strikes are 1 troy Pound (12 ounces) of Silver and may have some 24kt Heavy Electroplating or for the newer RWM mint strikes may have colorization.
$300 strikes are 1 troy Pound (12 ounces) of Silver and may have some 24kt Heavy Electroplating.