This site will explain:
* http://cash-and-treasures-wiki.travelchannel.com/page/Origin+of+Agates?t=anon
Moss Agate and Turritella Agate
semi precious
Agates can be found in various places around the world, including river beds, volcanic rocks, and areas with geothermal activity. Some popular locations for finding agates include the beaches of Lake Superior in the United States, the coasts of Brazil and Uruguay, and the state of Gujarat in India. Additionally, agates can also be found in certain regions of Australia, Mexico, and Germany, among others.
Agates are none of the above rock types, but a form of the mineral quartz, normally formed as a gas vesicle filler in igneous rocks, the microcrystalline quartz gradually filling the cavity with successive layers.
When potassium, magnesium, and manganese are mixed with water separately, they will undergo different chemical reactions. Potassium will react vigorously with water, magnesium will react slowly to produce magnesium hydroxide and hydrogen gas, while manganese will not react with water under normal conditions.
Californium don't react with water.
Curium doesn't react with water.
DDT doesn't react with water.
Protactinium react with water vapors.
As with most things, agate hunting is an acquired skill and simply reading the answer will not make you an expert! The following field guide will give you some tips on how and where to find agates on a pebble beach. Bret Fogelberg http://www.123agates.com/subpages/fieldguide.pdf
This is due to temperature and how water with different temperatures react.
Aluminum will not react with water at normal temperatures. Increase the temperature greatly, and just about any two things will react, though.