Hot answers tagged

19

which came first That's actually a very hard question. The most simple answer would indeed be igneous. Here's why: Sedimentary rocks (in the sense of rock cycle) comes from pre-existing igneous or metamorphic rocks, so you need to have had them first. Metamorphic rocks, by definition, are rocks that form from other kinds of rocks (be it igneous or ...


18

This is a chert nodule, which is often found within chalk (the white stuff). The darker stuff (the actual chert) is silica rich and the white stuff (the chalk) is carbon rich. Chert is often called 'Flint' if it is found within chalk, and depending on your location this may sound more familiar to you. As for the formation of this rock (which may or may ...


17

It's an interesting question, but in practice I think it's impossible to answer. It's very difficult to measure the rates of many of those processes, and the divisions between rock types can be quite ill-defined (for example, in migmatites). There's no scientific instrument we can point at a chunk of the earth which will tell us "in this region, 29.4 ...


15

Zeolites are very similar to clays, with one key difference. The molecular structure of clays is rather compact. In contrast, the molecular structure of zeolites has tiny molecular-sized holes, and these holes are wont to connect. The result is a porous, tunnel-filled structure at the molecular level. The resulting tunnels make zeolites very good at ...


14

How Japan Filled That Ginormous Sinkhole In Just One Week: The Fukuoka sinkhole measuring 8,700 square feet (808 square meter), 65 foot (20 m) deep: they poured a mixture of soil, water, and cement into the hole—they use more than 7,100 cubic meters of the stuff in all. YouTube timelapse. How To Fix a Giant Sinkhole about the two in Guatemala: The first ...


13

OK, so you've found yourself an interesting rock and you want to know how to identify it. I am going to go ahead and assume that you haven't studied Geology before (apologies if that's an assumption too far). The first thing you can do is to head to your local public library and find a basic "rocks, minerals and fossils" identification book, and try to ...


12

One can only speculate based upon a photograph - however they look very much like mineralized fractures. At some time in the past this rock mass may have fractured in response to thermal or tectonic stresses. Fluid may have then penetrated relatively long distances along the fractures into the area and infiltrated shorter distances into the wall rock along ...


12

the trick is not all isolated rocks are produced the same ways. Of the two in your pictures the first is an old volcanic events; intrusions, dikes, ect. depending on which rock in the region you are talking about. The whole deccan plateau region is full of them, some have been exposed on the surface via erosion. Basically everything else eroded faster than ...


11

The earth existed long before there were crustal rocks or a "rock cycle." The idea of the "rock cycle" has prerequisites to even be meaningful. These include : The existence of a crust (both a continental and oceanic crust actually.) Plate tectonics The existence of an atmosphere and ocean. Without all of these, the concept of the rock cycle (as ...


11

Generally you can't say what type of coal only by density (also, I don't know how you measured it and how accurate this measurement was). Anthracite differs from ordinary bituminous coal by its greater hardness, its higher relative density and luster which is often semi-metallic. By looking the geological map of the area, you can see some lacustrine deposits ...


11

The best way to learn about rock types is to handle rock specimens guided by an experienced geologist. By handling rock specimens you get to feel the weight of the rock, its roughness or smoothness or if it feels slippery, soapy, glassy, firm or crumbly. Is it weak or strong? You will also be able to better see the colours in the rock, the sizes of the ...


11

It certainly looks like rose quartz, but best to try a quick test. Chip off a small flake and see if it is hard enough to scratch glass. If it does, then it's almost certainly quartz. The translucence and vitreous fracture are also giveaways.


11

Mountains and rock do decompose or weather into sediment. A basic rock cycle overview shows the possible pathways between all three rock types (igneous, metamorphic, and sedimentary) how one type can be transformed into another. After a rock is weathered into sediment, that sediment can become a rock again. Weathering rates of rock vary widely regional ...


10

As far as I can judge from the picture, it is most probably slagstone, Swedish blue stone. Slag is a byproduct from ore smelting. In old foundries, the slag was molded and used as a constructing material for houses and roads. It is actually similar to obsidian, but is usually rather brittle. I believe that the hardness could be around 5-5.5, depending on ...


10

Bubble in an ancient lava flow What you're seeing is a vug in a vesicular basalt. A vug is simply a term for a mineral-lined cavity. In this case, the host rock is a basalt. You're seeing an ancient lava flow that trapped a bubble of gases escaping from the magma as it cooled. Over time, groundwater infiltrated the bubble. As the basalt was buried, ...


9

When learning to distinguish between siliceous and calcareous samples you should use a handlens. Look for quartz, feldspars or micas. Quartz clasts may be frosted, or you may be able to see conchoidal fracture. Calcite will be very soft compared to both feldspar and quartz, and should fail to scratch copper (or at least not scratch it very well, while a ...


9

According to page 86 of Exploring the World Ocean: In December 1989, ODP scientists drilled Hole 801C and recovered Jurassic-age rocks and sediments, about 170–165 million years old, from the Pigafetta Basin in the western Pacific, near the Mariana Islands. Sediments of nearly identical age had been found previously from the Deep Sea Drilling ...


9

This looks like a polymict (composed of fragments from different rock types) conglomerate, that has been polished. This rock is composed of many well rounded fragments of other rocks that have been eroded, transported and deposited in a new location. These fragments have then then undergone diagenesis (burial and compaction) to form the rock in the ...


9

Most meteorites are darker than this specimen, having a characteristic ablation texture on the unfractured surfaces. Admittedly, this specimen is weathered, which could lighten the surface appearance, but it has such a heterogenous texture, including non-spherical vugs, that it looks to me to be more volcanic than meteoritic in origin. The fact that it is ...


8

Since rocks can have magnetic signatures, as is the case with paleomagnetism, can they store past pressures also? Yes, but not directly, and it is very hard to know the exact pressure (in contrast with paleomagnetism where you can actually get a nice number). One way to do it is to simply look at the minerals you have in the rock. Some minerals exist only ...


8

The technical term for a sedimentary rock that has a lithified fine-grained sediment with larger pieces of rocks suspended in it upon lithification is a conglomerate. The fine-grained interstitial part is called the matrix, and the large pieces suspended in it are called clasts. Clasts can range from gravel- to boulder-size. These are technical terms used by ...


8

Your rock contains crinoid stem fossils. Wikipedia has a good summary of crinoids


8

The blue spots are natural. This rock is indeed granite from K2. The blue spots are azurite. Malachite is also reported from this same location. From Geology.com: "K2 granite is named after a mountain in the Karakoram Range near the border between Pakistan and China. K2, also known as "Mount Godwin Austen," is the second-highest mountain in the world. The ...


8

I can engage in some educated speculation about what you think you see, but I'm confident you were fooled by the shadows in the image, which are caused by a low sun angle and distorted by the terrain. These are not inuksuit (which is the correct plural of inuksuk). They are all natural, not man-made. Let's point out a few things we know and can see on the ...


8

Even rocks that have lasted for billions of years decompose when exposed to Earth's weather. What you have is indeed granite, but a somewhat decomposed granite, which is treated by geologists differently from the intact, solid stuff. The "crumbly bits" have their own name: grus. Granite is made of crystals of different minerals (mostly feldspar and ...


8

That's amethyst, a violet version of quartz See here


8

This is the key: used to be part It is important to look at this from a historical point of view. Up until the 1950s and early 1960s, there was no agreement to how granites form. This became the granite controversy. On the one hand, experimental work showed that granites crystallise from magma, but this magma had to be derived from basalt-like magmas. ...


8

Your rock is most likely colonial horn coral fossil. It is common fossil in middle Devonian Period in Kentucky. I won't venture a guess on species from just an image. Kentucky Geological Survey has a nice introductory guide to fossil corals.


7

Oolites are limestones that are usually considered as in-organic, although they may have bits of shell/etc in them. These form by the precipitation of calcium carbonate around particles (sand, broken shell, etc) with a process comparable to that of an oyster. Some oolite references: http://www.sandatlas.org/2012/09/oolite/ http://en.wikipedia.org/wiki/...


7

Looks like a epidote bearing skarn or tactite. Cornwall England is famous for tin and copper bearing skarns. Epidote is a common gangue mineral in these types of deposits. Skarns are typically formed at the contact zone between intrusions of granitic intrusion and carbonate sedimentary rocks such as limestone and dolostone. Decent summary of skarns can ...


Only top voted, non community-wiki answers of a minimum length are eligible