how to figure out what rock you have

One of the nigh common frustrations we have every bit rock collectors is identifying the cool rocks we find. It's fun to discover a cool-looking stone and add it to your collection, only it can often be hard to know exactly what it is you've establish. I accept plant that in that location aren't a lot of bang-up resources out there to help rockhounds identify their rocks, so I decided to put together this guide to aid you lot in figuring out what kind of rocks you've found.

To identify your rock, first take note of its physical properties like colour, luster, banding, layering, and grain size. Next, exam for hardness and weight by running simple tests. Finally, compare the properties of your rock to those of known rock types while looking for other identifying characteristics.

Identifying and classifying rocks can exist a catchy business. There is frequently a lot of room for interpretation and shades of grayness, but with some basic knowledge and skills, y'all tin normally state on a reasonably correct answer. I'll go into the full procedure yous should use, betoken you towards some useful tools, and give y'all some generalized pictures for comparing.

Analyze the Physical Properties of Your Rock

Rocks are classified based on their origin and their physical properties such as mineralogical composition, grain size, and texture. Observing and, in some cases, measuring these concrete properties is the beginning and well-nigh of import step towards identifying your rock. Get through each of these identifying properties and write down your observations. Depending on what blazon of rock you accept not all of these properties will be applicable, but most of them volition exist.

Once you take gone through this list of physical properties (it should simply take a few minutes), consult the tables I have compiled below to find the best match for your rock.

Color

I of the outset things yous'll find almost any rock is its colour. The color of a rock is often overrated when it comes to identification, but it is certainly an of import characteristic that should factor into the procedure.

Your stone may be one uniform color or information technology may have multiple colors. Make notation of every color you see, but y'all'll want to place the most emphasis on the most predominant one or ii colors. The dissimilar colors are due to the unlike minerals that your rock is comprised of, and by getting a crude estimate of the percentage of each colour in your stone you'll be able to make some inferences near its mineralogical makeup afterwards in this procedure.

Sometimes the color of a rock tin can be deceiving. Many people who are new to rock identification tend to lean too heavily on the color of a rock when trying to determine what it is. Always remember that colour is merely ane of many important physical backdrop and weigh information technology appropriately.

It's also of import to make sure you're looking at a relatively fresh surface on your rock. Some rocks volition appear very different on the outside than they practice on the inside because the exterior has been weathered and altered by the elements. If possible, break off a modest part of your rock to expose a fresh surface – especially if it looks heavily weathered on the outside.

Luster

Luster is a belongings that is more normally used in the identification of minerals. It describes the way light reflects off of a surface and tin exist very useful for description and identification.

In the case of your rock, we won't be using about of the terms and descriptions used for mineral identification. I just want y'all to take notation of how your rock generally seems to reflect light. Is it glassy? Ho-hum? Maybe a little sparkly?

Most rocks will fall under the category of 'irksome', only in that location are a few rock types that are easily identifiable based on glassy or slightly sparkly appearances.

Grain Size & Shape

One of the most important observations you should brand about your stone is about the presence, size, and shape of its grains.

When people think virtually rocks with grains they usually call back about sedimentary rocks. Clastic sedimentary rocks will frequently have visible grains of varying sizes, but in some rocks like shales and mudstones the grains are as well small to meet with the naked eye. You may need a magnifying drinking glass or jewel loupe like this one from Amazon in club to see very fine grains. Most chemic and evaporate sedimentary rocks volition not take visible grains.

Igneous rocks are subdivided into two categories that are expressed past grain size. Intrusive igneous rocks more often than not accept large, visible crystals because they cooled underground and the crystals had fourth dimension to organize and grow. Extrusive igneous rocks cooled more than rapidly on the surface, and therefore they won't have whatsoever visible grains.

For metamorphic rocks, the presence and size of grains is generally adamant by the protolith (the original, unaltered rock) and the degree of metamorphism. Sometimes when grains are present in a metamorphic rock they are the aforementioned crystals every bit were present in the protolith, only other times they are completely new crystals with unlike mineralogies, sizes, and orientations.

If visible grains are present, take note of the size distribution. Some rocks will be made upwardly of grains that are all the same size (or very close), while others will accept a variety of grain sizes. In sedimentary rocks, we refer to uniform grain sizes as 'well-sorted' while rocks with a multifariousness of grain sizes are referred to every bit 'poorly-sorted'.

It's also of import to detect the shape of the grains. Grains can be round, abrupt or angular, or everything in between. This holding is specially of import in the description of sedimentary rocks.

Foliation or Banding

The presence of foliation or banding is a very strong indicator that your rock is metamorphic. The rock will display what looks like banding, caused by the compaction and elongation of crystal grains.

This type of banding is but present in metamorphic rocks, so it tin really assistance narrow downwardly what type of stone you have. If at that place is no foliation or banding present then it is much more than likely that you have a sedimentary or igneous rock, because the grains are still more or less unchanged from their original shape.

It is important to distinguish betwixt foliation and layering. Foliation refers to the orientation of elongated crystal grains. All of the grains will exist stretched, and they will be lined up in one direction. If you lot look closely you will come across that there are no consistent layers that run through the rock. Instead, the rock is fairly uniform with the elongated grains interlocking with one some other.

Layering

This leads us to the adjacent important physical belongings to look for – layering. The layers you're looking for are parallel beds that may be straight or curved. The layers may be very thin (about 1mm) or up to several inches thick.

Well-nigh layered rocks are sedimentary, but some are metamorphic. Layering is seen only rarely in igneous rocks. Sedimentary rocks are ofttimes layered because of the style they are formed, and metamorphic rocks tin sometimes be layered if their protolith was. The presence and appearance of layering tin can exist a big clue when trying to identify your stone.

Hardness

The hardness of a rock can exist difficult to quantify because most rocks are fabricated upwards of several minerals which all have different hardnesses. Still, some basic tests tin can help narrow down what kind of rock you have.

In order to perform these simple tests, y'all'll need a piece of glass and a steel nail (or other piece of steel). You'll likewise exist using your fingernail, but I'll assume you already have those.

You can determine the full general hardness of your rock by whether or not it tin can scratch or exist scratched by your fingernail, drinking glass, and steel. Try to scratch one of your fingernails with the rock. If it leaves a scratch, move on to the glass and exercise the aforementioned thing (continue the glass on a flat surface and take care not to interruption it). If your rock scratches the glass, move on to the steel and encounter if the nail will scratch the rock.

Very Soft Rocks: Won't scratch your fingernail, drinking glass, or steel
Soft Rocks: Will scratch your fingernail, but won't scratch glass or steel
Medium Rocks: Will scratch your fingernail and glass, but won't scratch steel
Hard Rocks: Will scratch your fingernail, glass, and steel

Weight and Density

For purposes of identifying your rock, all you commonly need to practice is have annotation of how heavy the rock feels compared to other rocks its size. When you choice it upwardly, does it feel heavier than normal, lighter than normal, or about like you'd expect?

If you really want to get fancy you lot tin can perform specific gravity tests on your rock, but this is usually unnecessary. Because the mineralogy of rocks of a single stone type tin vary, the density and weight will vary correspondingly. For instance, the specific gravity of granite typically varies from 2.vii to 2.8 depending on the corporeality of quartz, feldspar, mica, and accessory minerals present.

Once again, for our purposes, just hold the rock in your paw and meet if it seems unusually light or heavy. This is usually enough to help with the identification process.

Texture and Feel

This test is a pretty easy 1, but it's also a fiddling subjective. Run your fingers over the surface of the stone and run into what y'all feel. Some rocks have textures that are unique plenty that they can aid in identification.

Most rocks volition just experience coarse or crude, merely if you experience something different be sure to make a note of information technology. Some rocks may feel glassy, slippery, greasy, or gritty. If y'all don't feel anything notable that's okay, as well.

Unique Identifiers

In that location are all sorts of other unique identifying characteristics that tin can help y'all identify your rock. Most of them are pretty specific and aren't seen in very many rocks, so I've grouped them together here.

We're looking for anything abnormal or that seems distinct nearly your rock. Things like bubbles in your rock, the presence of fossils, a reaction with weak acids, or interesting fracture trends can all help you effigy out what sort of rock you lot accept. These types of features are especially useful if you've already narrowed down your possibilities and you're looking for anything else that can refine your choices.

Compare the Stone'south Properties to Known Rock Types

At present that you have analyzed your rock and made note of every bit many physical characteristics equally possible, it's fourth dimension to actually find out what it is! Yous may already accept a very adept idea of whether your stone is sedimentary, igneous, or metamorphic, so I have divided the tables below accordingly.

Employ these tables to notice the rock type that well-nigh closely aligns with the properties of your stone. If you find a rock that is very close but doesn't quite lucifer, information technology may be worthwhile to go dorsum and re-evaluate the physical properties that don't align. Likewise, go on in mind that this list is far from exhaustive.

These tables are pretty comprehensive, but in that location may be uncommon rock types not listed hither. Follow the links for more than complete information on each rock type.

Sedimentary

Sedimentary rocks are made up of mineral particles or rock fragments that have been cemented together. They are normally readily discernable from igneous and metamorphic rocks past the presence of grains, layers, and/or fossils. Y'all can discover my post dedicated to sedimentary stone identification here.

Sedimentary rocks are typically subdivided into three groups:

Clastic sedimentary rocks are formed from stone fragments that have been cemented together.
Biochemical sedimentary rocks are formed from skeletons, shells, and organic matter.
Chemical sedimentary rocks are created when minerals precipitate out of solution.

Stone Proper noun	Composition	Grain Size	Hardness	Other Characteristics
Sandstone	Quartz, Feldspar	Medium	Difficult	Many colors, mostly chocolate-brown, tan, white, blood-red, yellow
Shale	Clay minerals, Quartz	Very Fine	Hard	Thin layers, normally gray to blackness, fissile
Siltstone	Quartz, Feldspar	Fine	Hard	Many colors, not fissile, lacks clay minerals
Mudstone	Quartz, Feldspar	Very Fine	Hard	Non fissile, no layers, sometimes refers to limestone
Limestone	Calcite, Aragonite	Very fine	Soft	Oft contains fossils, fizzes with acid, ordinarily white or grayness
Dolostone	Dolomite	Very fine to medium	Soft	Frequently confused with limestone. Only slight fizz on fresh surface
Breccia	Varied rock fragments	Fine to very large (varied)	Soft to difficult (varied)	Similar to conglomerate, merely with angular grains
Conglomerate	Varied rock fragments	Fine to very big (varied)	Soft to hard (varied)	Like to breccia, but with rounded grains
Arkose	Feldspar, Quartz, rock fragments	Medium to coarse	Difficult	Normally gray or cherry-red, similar to sandstone, only more feldspar
Greywacke	Quartz, Feldspar, stone fragments	Very fine to coarse (varied)	Hard	Dark greyness colour, angular grains, many grain sizes
Wackestone	Calcite, shell fragments	Very fine	Soft	Grains supported in mudstone
Coquina	Trounce fragments	Medium to large	Medium to difficult	Mostly shell fragments, can be poorly- or well-cemented
Evaporite	Halite, Gypsum, etc.	Coarse	Very soft	Rock formed from soluble minerals and evaporation
Chert	Quartz	Very fine	Difficult	Many colors, no visible grains, conchoidal fractures
Oolite	Calcite, Aragonite	Medium to large	Soft	Fabricated of round 'ooids', tin can be white, gray, reddish

Igneous

Igneous rocks are formed from the cooling and solidification of molten magma or lava. Their composition is adamant past the chemical limerick of the lava or magma from which information technology forms, while the degree of crystal formation is adamant by the amount of time it takes for the magma or lava to absurd. In addition to this article, you can find my mail service defended to igneous rock identification here.

Igneous rocks are subdivided into two general groups:

Extrusive igneous rocks are formed from rapidly cooling lava on the surface.
Intrusive igneous rocks are formed from slowly cooling magma below the surface.

Rock Proper noun	Composition	Grain Size	Color	Other Characteristics
Granite	Quartz, Feldspar, Mica or Amphibole	Fibroid	White, Pink, Gray	Color and grain size highly variable
Rhyolite	Quartz, Feldspar	Very fine to burnished	Light color	Very high silica content, may contain larger crystals (phenocrysts)
Diorite	Plagioclase, Biotite, Hornblende, Pyroxene	Coarse	White and dark grayness	Fairly rare, oft dislocated with gabbro
Basalt	Augite, Pyroxene, Plagioclase, depression-silica	Fine	Dark gray, sometimes lite	Often has gas bubbling (vesicles). Can contain some larger crystals (porphyritic)
Diabase	Plagioclase, Augite, Olivine	Fine	Gray to dark grayness	Sometimes called 'microgabbro'. Fine but visible crystals
Gabbro	Augite, Pyroxene, Plagioclase, low-silica	Coarse	Gray to dark grayness	Intrusive equivalent of basalt
Pumice	Highly varied	Very fine, glassy	Light	Many small gas bubbles (vesicles), floats in water
Scoria	Augite, Pyroxene, Plagioclase, low-silica	Very fine	Nighttime	Larger gas bubbling (vesicles) and vesicle walls than pumice. Usually does not float.
Obsidian	Quartz, feldspar	Glassy	Dark, light (rarely)	Conchoidal fractures, very sharp edges
Andesite	Plagioclase, Pyroxene, Hornblende	Fine grained, som large	Low-cal to dark grey	Between basalt and rhyolite. Porphyritic texture (some large crystals)
Tuff	Highly variable	Very fine	Low-cal to nighttime	Relatively soft, made of volcanic ash
Pegmatite	Quartz, Feldspar, Mica	Coarse to Very big	White, Pink, Grayness, Varied	Resembles granite, but fifty-fifty bigger crystals
Syenite	Alkali Feldpsar	Coarse	Light to medium	Similar to granite but defective quartz
Dunite	Olivine, Pyroxene	Coarse	Greenish	Fairly rare. About entirely olivine crystals

Metamorphic

Metamorphic rocks are formed when existing rocks are subjected to heat and pressure level, changing their shape, appearance, and composition. They are ofttimes distinguishable from other rock types by their foliation and the presence of characteristic metamorphic minerals like garnet, kyanite, and staurolite.

You tin can find my complete mail service most metamorphic rock identification here.

The type of metamorphic rock that is created depends on the original stone (known as the protolith) and the temperatures and pressures to which it has been subjected. Some rocks undergo multiple stages of metamorphism.

Metamorphic rocks are often loosely classified into three groups based on their texture

Gneiss – Coarse grained, thick (>5mm) foliation
Schist – Medium grained, strongly foliated
Granofels – No apparent foliation

Stone Type	Composition	Grain Size	Foliation	Color	Other Characteristics
Gneiss	Quartz, Feldspar, Mica, Varied	Fibroid	Yes	Light and dark	Alternating bands of light and dark
Schist	Mica, Chlorite, Quartz, Feldspar, Varied	Medium to Coars	Yes	Light to dark	Platy, flaky texture. Defined by texture, so composition is highly variable
Marble	Calcite, Dolomite	Fine to coarse	No	Usually white, with swirls of other colors	Soft, metamorphosed limestone or dolostone
Quartzite	Quartz	Medium	No	White, Gray, Pink	Hard, metamorphose sandstone
Slate	Clay or volcanic ash, Quartz	Fine	Yes	Grayness	Sometimes dislocated for shale
Serpentinite	Serpentine, Brucite, Magnetite	Fine	No	Calorie-free to dark green	Greasy feeling
Amphibolite	Hornblende, Actinolite, Plagioclase	Medium to fibroid	Yep, weak	Night	Dense, very little silica
Granulite	Feldspar, Quartz, etc.	Medium to fibroid	No	Light	Crimson or pinkish garnet crystals mutual
Hornfels	Varied -Clays, Quartz, Feldspars, Hornblende, Calcite	Fine	No	Varied from light, night, green, etc.	Very hard, originally sandstone
Skarn	Calcite, Dolomite, Garnet, Pyroxene	Fibroid	No	Low-cal to medium	Very difficult, tin can course from sedimentary or igneous protolith
Soapstone	Talc, Chlorite, Amphibole	Fine	No	Light	Schistose or massive texture. Very soft, may feel like soap
Migmatite	Varied – at to the lowest degree two singled-out stone types	Fine to medium	No	Lite and dark	Clearly visible layers that may appear 'melted'

Utilize Available Stone Identification Resources

If y'all're gone through the identification procedure I outlined above, chances are yous'll be able to get a solid answer about what type of stone you have. Notwithstanding, there are some additional tools available that could assist you in the process.

Some of these tools I have constitute very useful, while others are hitting-and-miss. If you cull to use any of them I would still highly recommend making a annotation of all the physical properties of your rock that I outlined above.

Here are some of the most popular stone identification tools bachelor:

Smithsonian Handbooks: Rocks & Minerals – This book is the almost useful I take found for help in identifying rocks and minerals. It has gorgeous pictures and nice descriptions of hundreds of rocks and minerals. The but drawback to a book similar this is that it tin sometimes be difficult to sift through to notice a rock that matches yours. Even if you have gone through the process of documenting your rock'due south physical backdrop, it can take a while to match it with a rock blazon in the volume.
The Rock Central – This tool is a petty dated merely the concept and information is great. Using many of the physical properties I listed above, you just answer questions about your rock and it moves through a menstruation chart until you land on an answer. Information technology's a little simplistic and doesn't cover every blazon of stone, only for most major stone types it works very well.
Stone ID App (Google Play) – This app uses AI and image recognition algorithms to identify what kind of rock you have. You can also observe it on the Apple shop here. I take found that this app (and others like information technology) are unreliable, merely your mileage may vary. They rely on sophisticated algorithms that compare an epitome of your rock (taken from your telephone) to thousands of others. Sometimes information technology works, and sometimes information technology doesn't. If nothing else, it's fun to play effectually with!
What Is The Rock? Subreddit – This is a place defended to trying to figure out what kind of rock yous have. It is ofttimes difficult to tell what a rock is based solely on pictures, so they more data you can provide (similar the physical backdrop I listed in a higher place) the better. Accept nice, well-lit pictures from multiple angles and and so make a mail on the subreddit. Users (possibly even me!) can then hash out and make a best guess nearly what kind of stone yous have.

By the mode, if yous desire to learn all yous can most rocks and minerals, I would highly recommend subscribing to Rock & Jewel Magazine. They have great articles from knowledgeable and respected geologists and gemologists all most rock collecting, faceting, field trip ideas, and projects for kids. It'southward a must for any aspiring rockhound!

Go an Outside Opinion, if Needed

If you lot have gone through all of these steps and you lot still haven't come to a satisfactory answer, there are some additional measures you can take. Geology can be absolutely crazy sometimes, and there are a lot of rocks out there that tin can stump fifty-fifty the most experienced rockhounds.

The first affair I would suggest is to take your rock to a local rock store, rockhounding club, or the geological survey for your state or country. You'll find some experienced geologists and enthusiasts at these places that are likely extremely familiar with the local geology. This is especially helpful if you institute the rock locally – chances are that you'll exist able to detect someone who has seen a rock just like yours.

Consider Culling Explanations

I would suggest you not to get besides hung up on rocks that 'look strange'. Some rocks have odd shapes or features that exit people scratching their heads. While these features can sometimes be useful for identification, they are oftentimes more distracting than anything else. Stay focused on the physical properties listed in a higher place when trying to identify your rock.

One last affair to consider is that what y'all constitute may not be a rock at all. I often come across people posting pictures online request for help identifying their 'stone' that is actually slag (a waste material formed from smelting), manmade brick or physical, or colored glass. These types of finds tin can be really absurd looking just can exist confusing when people think they've plant a rock.

In a similar vein, your rock may be a unmarried mineral type. If you've found a crystal, gemstone, or other uniform-looking rock (especially if it displays any sort of crystal structure) y'all may be barking up the incorrect tree. The rock identification methods in this article won't be of much use, and then you should instead use mineral identification techniques.

davidsonshypeation.blogspot.com

Source: https://rockhoundresource.com/how-to-identify-your-rocks-full-guide-with-helpful-tools/