Herkimer Diamond Mining
Popular with collectors looking for large crystals, but all sizes and types of crystals can be found here.
Mix of sun and shade
Dirt digging and hard rock breaking
Guided prospectors and machine digs available
Chance of finding museum-quality specimens
Known for large Herkimer diamonds
Primitive camping available
Hillside location with beautiful scenery, but steep
Open year round
Largest crystal that I found at Mohawk Valley Mineral Mining (pic)
Sprakers, NY 
Nice family run operation on a small private site.
Mix of sun and shade
Chance of finding museum-quality specimens such as rare crystal varieties including black stem scepters, skeletal crystals, and "black diamonds"
Owners help location a potential crystal baring rock and dirt
Dirt digging and hard rock breaking
Little Falls, NY
It is geared toward people looking for exceptional specimens. Best for collectors who want the possibility of finding exceptional or valuable crystals and don't mind paying for a premium experience.
Forested property with significant shade
Combination of dirt digging and hard rock breaking
Prospector available to help beginners locate productive areas
Chance of finding museum-quality specimens such as rare crystal varieties including black stem scepters, skeletal crystals, and "black diamonds"
Little Falls, NY
One of the newer premium mining experiences with excellent natural surroundings and a strong emphasis on guided collecting. Visitors who want a premium guided experience without the crowds found at larger commercial mines.
Large amount of shade from surrounding forest
Dirt digging and hard rock breaking
Experienced prospectors help visitors get started
Good opportunity to find high-quality crystals
Only open on selected weekends
Fonda, NYSt. Johnsville, NY
Often considered one of the better places for beginners because crystals are found in several different types of digging areas. Families, beginners, and collectors who enjoy display pieces with crystals still attached to the host rock (matrix specimens).
Inexpensive admission
Dirt digging and hard rock digging
Easier to find crystals
Most crystals remain attached to the surrounding rock (matrix)
Campground available
Can be very sunny and hot, although some shaded areas are available
Middleville, NYThe oldest and most famous public Herkimer diamond mine. A good first experience for those who do not want to spend much time or money.
Least expensive
Excellent facilities
Basic experience breaking hard rock
Very little shade
High-quality specimens are very difficult and require experience
Equipment rentals available