I have a few hundred of them so I have studied a decent sample.To generalize the eyes usually only go into the stone the distance of about half the eyes diameter. Many times the eyes on a stone are situated 120 degrees from each other and if the stone is fairly narrow the eyes can touch internally. Most agates that have eyes have an oxidation patina on the outside which gives the eye color and contrast but if you cut through the altered surface the remaining eye is merely clear agate. A small percentage of the Gobi agates are like that but most have eyes that incorporate iron or copper to give rich saturated color that goes below the surface of the stone.There are two places in north America with similar but less baroque agates but the Gobi agates seem unique in that they incorporate metal ore during their formation rather than as a post formation weathering phenomena. Monte Lake B.C. Canada is a beautiful tourist destination where similar eye agates can be collected with the caveat that most are broken and incomplete as is the norm everywhere they are found.