A guide for asking "Identify this rock" questions?

Question

Spurred on by the discussion on my earlier question about whether or not 'identify this rock' questions should be on topic and the appearance of our first such question; I propose that we make a guide so that we can refer people to it when appropriate.

I'll start a community wiki answer to this question where I'll put in a few of the basic things that I know about. I'm not a geologist though, so I'll need you guys to fill in most of the details. We should try to rely on tests that the average person can do reasonably quickly in their own home.

Answer 1

As of 2019-07-30, Rock identification questions are off-topic on Earth Science Stack Exchange. Please see this meta post.

Please find another forum for your question. When you do find another forum, please do refer to the underlying guide, as it is universally useful regardless of where you ask.

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How to ask an "Identify this rock" question

This guide is refered to rocks. If you think you have a fossil and not a rock, follow this guide

Example of a good question for a rock.

1) Describe where you found it

Be as specific as you can (just country or state is not enough!). What part of the world? Was it on a beach? Did you find it lying on top of the ground or did you have to dig for it? Were there lots of them around or was this the only one? Note that if you got the rock as a gift or you bought it, you won't be able to provide a location, so your question will most likely be closed as "off-topic".

If you can, post a picture of the place where you found it. Let us a link to Google Maps or another online mapping service, with a pin on the exact place (single click on the place to pin, and copy the URL). Some places are covered with Google Street View and this may allow us to take a look at the place.

2) Post a well-lit, sharp photo with a scale

Take a sharp photo in bright white lighting next to a scale or ruler of some sort. Try to use daylight (but not direct sunlight) or bright white fluorescent lights. No flash. Make sure that the rock is well lit but don't saturate the image. If possible, use a plain background, such as a sheet of white paper. Also remember to either get the units of your scale in the picture or post it in the question. If the rock has a visible crystal structure, make sure that it is clearly visible in the photo.

If the piece is a rock and not valuable, break it an picture a fresh surface, as suggested here.

Note: while a good photograph is important, it is not a substitute for a written description. Images of unknown things cannot be searched. For search purposes, questions should provide an image, and also describe the image in as much relevant detail as possible.

3) Describe its properties

If you have broken your piece, describe the properties at the fresh surface.

What color is it? What kind of lustre does it have? Is it made up of layers? Can you see grains? How easy is it to break pieces off? How homogeneous is it? Does it seem unusually light or heavy for its size? Does it leave any streak on a paper?
Name its main property (color, structure) in the title (as suggested here).

3.1) Test its hardness

Test the mineral’s hardness on the Mohs hardness scale. This is pretty easy to do by comparing it to some common household items. The list below gives the hardness of some common objects; if these objects can scratch your rock, then the rock is softer, otherwise it is harder.

• Fingernail: 2.5
• Penny or other US coin: 3
• Knife blade: 5.5
• Glass: 5.5
• Steel file: 6.5
• Quartz: 7
• Diamond: 10

3.2) Measure its density

Weight it and measure its volume as shown here, so we will know its density.

4) Be prepared to answer follow up questions

More than likely some more information will be needed to identify your rock. Users will post clarification question in the comment section of your answer. If the questions only need a one line answer, then leave it as a comment. If the question requires a longer answer, then edit your post to include the additional information.

5) Tag your question with identification-request

This tag will help identify your question as a identification question and make it easier to find for people that can answer your question.

6) Name your question in a relevant way.

"Help me identify this rock" or "Rock identification needed" are very unspecific, and won't help you get good answers. A title like "Rock ID: soft, white, from Dover, UK" will help your question to stand out, and will also make it more interesting to experts in the region, who might have a better idea about the geology of their area.

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Why was my question closed as "off-topic"?

If your question doesn't address the points above, it makes the question vague with many possible answers and low confidence. If you haven't responded to comments and have not provided enough information, your question will likely be closed as off-topic. If this happens, please edit your question to include the things above, which will automatically nominate it be reopened.

Answer 2

A streak test is another test that can be useful in mineral identification. If you are able to perform this test, include the results in the question.

Streak is the colour of the powdered mineral. In many cases it is the same colour as the rock but in some it is very different from the normal surface.

To perform a streak test, you need a piece of hard, white, unglazed porcelain, ideally with a slightly rough surface. Geologists use specially made pieces called streak plates but you can often use the bottom of a cup or plate. If the bottom is glazed, use the unglazed foot-ring if it has one. Be careful that the pot is harder than your mineral or rock, otherwise you will just see the powdered porcelain (look to see if you have scratched the pot).

Rub your mineral on the streak plate to produce a powder and describe the colour. Some minerals with diagnostic streak are:

pyrite: Brassy-coloured surface but produces a grey streak.

hematitie: Often grey colour but produces a red or reddish-brown streak.

goethite: Often grey colour but produces a pale yellow streak

ilmenite: grey to black producing a black streak

flourite: May be white, green, purple, or clear but produces a white streak

Answer 3

Describe and photograph a fresh surface.

Breaking open a rock to see an unweathered surface is very important for identification. In some cases the minerals show up better on a weathered surface so include both pictures if possible.

This isn't as important for mineral crystal specimens and we understand if you are reluctant to destroy your sample but not seeing a fresh rock surface will make it hard to answer your question.

Look at and photograph the surface when wet and dry.

Geologists often lick or spit on rocks to bring out features that are hard to see on dry surfaces (you could also use plain water). Do not lick rocks that might be toxic like some ore samples.

Answer 4

They are little differences for the four posible cases: mineral, rock, fossil, antropogenic.

In the geological point of view, what a geologist needs is a good picture and a precise location. If he can make a picture of the outcrop better. If the poster tells me his location, some countries has not only an application to know what geological unity is, but sometimes a cartographic map and a pdf where the geologists explain the local geology. This can lead in some cases to a inmediate identification, whereas discussion uses to be between two or three posible minerals/rocks.

eg someone posted a picture from north of Ireland. I can take a look at Ireland Geological Survey Then collectionists may not be very interested, but it can not only help to determine the piece, but to give an age (specially important in paleontology), and write a little geological history for the students.

It migth be interesting to add things at point 3. url on maps. or geological unit if known. Picture of the outcrop if possible. And then, for minerals and fossils it is not a good idea, but for rocks, fresh surface picture matters as said.

For a rock it migth be fine, it they have an augmentation glass, to tell them to describe what minerals they see, but I think this is too much to ask them to do if they are not geology related. I don't know how much far can we see texture if the picture is high quality and allows zoom; for a rock this is esential. If they put a rock and a bad picture and say "Hey, what's this rock?". "Yeah that looks a sandstone" we can say them, but to classify it you need to see the quartz grains. Size, rounded, translucents, matrix?. With the pictures they use to provide it is completely impossible to classify correctly a rock.

Answer 5

If you think you have a fossil, Use this guide instead.

1. You may not have a fossil

This is always a possibility there are many chemical and physical processes that look superficially like fossils. If multiple comments tell you it is not a fossil be expected to supply the information from the other guide and retag your question. You may even find reposting it is easier.

2. Post a well lit sharp photo with scale, preferably from multiple angles.

Take a sharp photo in bright white lighting next to a scale or ruler of some sort. Try to use daylight (but not direct sunlight) or bright white fluorescent lights. No flash. Make sure that the rock is well lit but don't saturate the image. If possible, use a plain background, such as a sheet of white paper. Scale is important many shapes reoccur in nature and belong to completely different organisms. Scale can best be provided with a grid scale bar but not everyone has one of those, failing that a lined ruler or tape measure either on the object or on whatever the object is resting on is best. Failing that at least include a standardized object like a battery or coin.

Multiple angles is important as the goal is to recognize the three dimensional shape of the fossil. Shape and appearance are the single most distinguishing feature for fossils. If the fossil is already broken include an image of the broken section but do not break the fossil further. Fossils are often very fragile and may simply disintegrate if repeatedly broken. Do not scratch or streak a suspected fossil it will not provide useful information and only damages the fossil.

3. Describe where you found it.

Be as specific as you can (just country or state is not enough!). What part of the world? Was it on a beach? Was it in a particular formation or known deposit? Were there lots of them around or was this the only one? Often similar fossils are distinguished easily by locality. If possible photograph the fossil in place.

4. Include a description

While photos are better a description can provide useful information, Is the fossil porous, does it have layering? Is there a recognizable surface pattern or texture? This also important for searchability it is easier to search words than photos.

5. Be prepared to answer follow up questions More than likely some more information will be needed to identify your Fossil. Users will post clarification question in the comment section of your answer. If the questions only need a one line answer, then leave it as a comment. If the question requires a longer answer, then edit your post to include the additional information.

6. Tag your question with identification-request and fossil

These tags will help identify your question as a identification question and make it easier to find for people that can answer your question.

7. Name your question in a relevant way.

"Help me identify this rock" or "Fossil identification needed" are very unspecific, and won't help you get good answers. A title like "Fossil ID: jaw bone, from Dover, UK" or "Fossil ID: flat angular plates in chalk" will help your question to stand out, and will also make it more interesting to experts in a specialized area who may have more familiarity with a locality or group of organisms. One paleontologist may be able very familiar with marine species but not be able to identify plant remains any further than "plant". For this reason it is also recommended you not accept an answer right away but give a while for others to review it.

Note Collecting fossil material on government land is illegal without a permit in many countries (US included), please do not collect(remove) fossils if you do not know the laws in your country.