crownedrose:

Geology (by reardwen)

A single specimen containing the whole history of change at the Earth’s surface. If you go to the largest print, you can read the information label (a bit fuzzy on the right). Contains Calcite, Sphalerite, galena, and strontium sulphate.

(via geologise)

mineralia:

Galena with Chalcopyrite, Dolomite, Calcite from Missouri

What is a Geode?
(photo from scientificsonline)

These aren’t just any rocks! On the outside, it doesn’t look like much to many people. They seem like any ordinary rock you pass by constantly on your daily travels, but on the inside there are hidden worlds full of the most beautiful formations. It’s like having a mini crystal cave right in the palm of your hand! Of course, these rocks can also grow to massive sizes, but many can be easily bought to sit right on a table for display.

So how do these geodes form? These structures occur when minerals are deposited in sedimentary and some igneous (of volcanic origin) rocks that contain cavities and gas bubbles, allowing these then minerals (like carbonates and silicates) to dissolve and form inside the hardening surface that encloses the chamber. As time goes on, groundwater and hydrothermal circulation allows the perfect setting for crystals to begin forming within the rock’s hallow cavity.

A geode shell usually consists of Calcedony, where the interiors can contain a wide variety of minerals and crystals like Quartz, Calcite, Barite, Amethyst, Agate banding, Jasper banding, Celestite, Dolomite, Pyrite, Sphalerite, Smithsonite and more. Sometimes geode slices can be artificially coloured or morphed to enhance different banding and layers to appeal to buyers. Though the best kind of geode is a natural, unaltered geode!

Calcite from Cumbria, England (by hyperion327)

Calcite In Amethyst Geode (by hyperion327)