I know that we dig for crystals and ore but I wondered how they got there and especially how crystals would slowly creep up from deeper areas of the ground to higher ones.
Another question I want to add is, can this occur suddenly?
The definition of “suddenly” is a big vague in geology terms so I’d be interested in: could it happen “suddenly” in a day, week, month, year and if so – how?
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I don’t think they “creep”. The principal of superposition tells us stuff closer to the surface is newer than things deeper in the ground.
The only thing that I think could affect this at all quickly are certain plate tectonics pushing material upwards like mountains etc.
Metal ores are pretty much just rocks which have higher than usual concentrations of certain elements. They still require a lot of processing after mining in order to extract the element(s) of interest.
Mineral crystals of the sort that people go looking for as collectibles often form in cavities in the rock or ground – these can be from gas bubbles which didn’t quite escape the rock when it was molten, or cavities which exist in the soil due to tree roots breaking up the ground. Anyway, a cavity lends itself well to the unobstructed growth of crystals as water leaches through and deposits stuff that was dissolved in the water. The lack of obstruction to growth means crystal faced can develop well.
If an area is uplifted in general then weathering and erosion will wear away the top layers and things inside will gradually get exposed. Uplift may occur due to long term tectonic forces – most obviously in mountain belts, but also just sections of the upper crust not associated with mountains, or blocks of crust like the horsts in [horst and graben structures](https://i.imgur.com/mlcke8O.gif) are effectively uplifted compared to the surroundings and so experience more weathering. [Post-glacial rebound](https://en.wikipedia.org/wiki/Post-glacial_rebound) is another factor which can causes uplift. Then there are cliff faces which experience a fair amount of weathering just from being exposed – fossil hunters often go to such areas after storms to see what new things have been uncovered.
One last thing to mention is any place that has winters cold enough to freeze the ground might experience the seemingly magical appearance of rocks welling up from beneath the surface. This is so common in the eastern U.S. that they became known as “New England potatoes” by the farmers there.
Rocks are better conductors of heat than soil, so the rock conducts heat away from the warmer soil beneath it. That colder soil under the rock then freezes before other dirt at the same depth.
Remember that when water freezes it expands. So, when the water in the soil under the rock freezes, it expands and pushes the rock up a little.
When the ground thaws a space is left under the stone which fills with dirt, so the stone rests a little higher. Over a period of time this repeated freezing, expanding, upward push, and filling underneath eventually shoves the rock to the surface.
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