Opals require special care due to their structure. You do not want to use harsh chemicals to clean them and they should be stored separately from other gemstones that may scratch them. If you have a cloth pouch, this would help separate the opal from metal jewelry or other gemstones.
It has been known that opals stored in a dry environment, such as a bank vault, have developed a series of minute cracks called crazing. This can also happen due to the structure of the opal and how it developed in the ground. Some advise the opal to be stored in oil to prevent crazing, but this is more lore than fact.
As for the value, there are many various types of opals and each would be evaluated accordingly. An educated and experienced gemologist, such as the Certified Gemologist or Certified Gemologist Appraiser of the American Gem Society can best advise you about this October birthstone.