July's Birthstone is Ruby. The two rubies below are from the shop. The first is ruby in marble matrix from Pakistan and the second is a ruby crystal from Madagascar Ruby is a variety of corundum, the other gem variety of corundum is sapphire.
For more info on Ruby mineral data: Corundum: The mineral Corundum, Sapphire, Ruby info & pictures
The most frequent question I get when customers purchase ruby and sapphire is "can I have this cut for jewelry?" When you examine a gemstone sample note its clarity and color - no amount of cutting and polishing is going to improve the color or clarity. The best are facet grade rubies and generally these will not be offered as mineral samples because of the greater demand from the jewelry market. When a mineral is demanded in more then one market the forces of competition escalate the price. The Madagascar ruby below is jewelry grade - rubies of this quality and from this deposit are polished into beads and cabochons. The Pakistani one is also pretty good but the rubies from Pakistan tend to get murkier (occluded) the larger they get. In today's market Ruby mineral specimens are readily available from Pakistan, India, Madagascar, Afghanistan and Vietnam. They are occasionally available from Burma (Myanmar) though because of the excellent quality they are quite expensive.
Many gemstones are oiled or heat treated. This is a generally accepted practice in the jewelry market but is unacceptable in the mineral market. It can be difficult to determine if a mineral specimen has been tampered with. Ask the dealer. Dealers sometimes do get snookered but a good mineral dealer keeps up with current literature and gossip to be aware of malfeasance. In either case, mineral or jewelry, any "enhancements" should be disclosed.
A good article on color in rubies:
Ruby - About Colored Gemstones
World Famous Rubies: The Delong Star Ruby
The Midnight Star Ruby
The Mogok Ruby
The Rosser Reeves Star Ruby