# Tag Info

12

It's a piece from a catalytic converter of the exhaust system that was in a car. Specifically the internal catalyst support, which is ceramic. It looks like someone burned off the actual catalyst from the ceramic support. I see them all the time at the scrapyard where I get steel.

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 ...

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, ...

10

This is artificial glass. Pink transparent obsidian does not exist in nature, despite what some people who sell it say.

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 ...

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

Very interesting pictures. I will go out on a limb and say it looks like it is mostly barite (barium sulfate, $\ce{BaSO_4}$). The clear ball-shaped crystals may be celestite (strontium sulfate, $\ce{SrSO_4}$). Barite often forms tabular crystals and is very dense. It is used in drilling mud for oil wells because it can help hold in the pressure. The ...

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

The pendant might be dyed howlite, a common fake for real turquoise. The most distinguishing tests are destructive. Hardness test: (THIS IS A DESTRUCTIVE TEST.) A steel knife blade will easily scratch howlite which has Mohs hardness value of 3.5 Turquoise has Mohs hardness of 5–6 BEWARE: Knife blade can still scratch turquoise. YOU HAVE BEEN WARNED. Dye ...

7

The boulder is a sculpture; the rock type is almost certainly conglomerate, a kind of sedimentary rock. Quoting here from an article about a geology walk, by Jean Gardner, in the winter 2014 newsletter of the Hertfordshire Geological Society: [The] boulder is a conglomerate containing well rounded metamorphic and some igneous clasts ranging from ...

7

The colour, crystal morphology and twinning strongly suggests rutile (titanium oxide). Please see MinDat.org (e.g. http://www.mindat.org/gallery.php?cform_is_valid=1&min=3486&cf_pager_page=36) for examples

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 ...

7

Almost certainly quartz. But it looks like it's most likely from a quartz vein not quartzite which is metamorphic. I have seen quartzite that looks like that but most often it has a more granular texture. It may be impossible to know for sure unless you can rule out quartzite because of the location. Where was it found? Please see our guide for asking, '...

7

Your rock is an exceptional sample of molybdenite. According to this USGS report, Mt Shasta (Yellow Butte?) contains some molybdenite. Your description of the rock being silvery and crumbly is consistent with it being molybdenite. The picture shows cleavage and the platy crystal morphology. You could confirm it by trying to bend some of the thinner "plates"...

7

Your mineral specimen is most likely goethite after pyrite, a common pseudomorph found in many different geological environments. A quick google search revealed pyrite and goethite can be found in Normandy. Mindat - Goethite (map before from Mindat) Soumont-Saint-Quentin mine, Calvados, Normandy, France

6

When you say that it scratched quartz, do you mean that it left a mark on it? Can you wipe that mark off, or does it stay on the quartz? It may actually be the streak of your stone on quartz. Also, try to scratch your stone with quartz (the reverse of what you did) to confirm your observation. If your stone is indeed harder than quartz, then my guess that ...

6

The lower picture has a surface texture similar to some agates. It has a colour somewhat resembling fire agate, but it is difficult to be sure without examining a thin section under a polarizing microscope. True opal is an amorphous gel of silica and water, and hence is isotropic.Hence, it appears black under crossed polarizers, whereas agate is ...

6

This rock is most definitely a conglomerate. The grain size appears to be bimodally distributed with pebble sized clasts in a coarse sand matrix. The grain shape for the clasts appears well rounded and a medium sphericity. A quantitative analysis of grain size can be obtained by randomly selecting grains and measuring them (both the clasts and the matrix). ...

6

One really needs to examine a rock under a polarizing microscope to say very much about its composition and history. As you rightly say, it's very obviously a medium to high energy conglomerate. Judging from the heterogeneous lithology of the individual rounded particles, one might infer that it is a fluvial sedimentary environment, such as an alluvial fan, ...

6

It is a quartz crystal artificially coated in thin layer of metal called aura quartz or rainbow quartz. They come in various colours and often can be found in new age shops. More information on the topic can be found on wiki: https://en.wikipedia.org/wiki/Metal-coated_crystal

6

Based on the photo, your rock is not a meteorite but a piece of lead ore containing galena. Even with a blurry image, I can see well defined cleavage planes. Galenam, lead sulfide, is the most common grey metallic mineral with showing perfect cleavage. Galena is also very dense. Ref: Galena Mindat.org.

6

Your rock is quartz crystal covered in very pale purple amethyst, which is also a variety of quartz.

6

That’s labradorite, it’s a silicate and a type of plagioclase feldspar named after Labrador, Canada. The iridescent colours that are seen is called the “schiller” effect. It is caused by light being scattered by thin layers of feldspar within the rock that formed as it cooled.

5

Argillaceous Siltstone. Sedimentary rock made from silt with a grain size bigger than that of clay but smaller than sand.Siltstones often show bedding planes and even ripples, where successive layers of silt have been deposited.

5

It is always hard to tell without seeing the actual rock but it appears from the fresh surface to be a mixture of dark grey/black and light grey/white crystals that are prismatic in shape - with rectangular cross sections. Thus it seems to me to be a mafic (meaning dark) intrusive (not erupted to the surface but cooled slowly underground so the crystals had ...

5

Given the photographs and the additional information you gave in the comments, I would say that this is specular hematite. Hematite is iron ore - its chemical formula is $\ce{Fe2O3}$. It's a mineral that's usually red-brown, but in some cases it appears shiny with a somewhat metallic lustre - that's the "specular" bit in it. The streak of hematite is red-...

5

Quoting from mlra66 Flickr page Monolith and Shadow by John Aiken University College Hospital, Euston Road, London. The monolith is made from a recently discovered Brazilian granite - a rich and exotic stone that combines many colours, shapes and patterns. The decorative elements represent minerals ranging from granite, flint and quartz to precious and ...

5

I would go with tufa - freshwatter CaCO3 deposit. Check if reacts to 10% HCl

5

I agree with Imorgh, that it is almost certainly a bit of freshwater limestone. It contains the botryoidal open-space depositional texture, and other irregular 'flowstone' textures that one associates with carbonate deposition around roots, leaf litter and other organic remains. Over time the organics oxidize and disappear, leaving just the porous carbonate ...

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