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Mineral identification is a captivating pursuit for both avid collectors and dedicated scientists. Whether you’ve unearthed a mysterious rock on a hike, purchased a beautiful specimen at a mineral show, or need to identify a sample for research, understanding the methods of mineral identification is essential. The approach can vary depending on the type of stone and your specific goals.
In the field, simple observations of physical properties like luster, hardness, and color can often lead to a positive identification. However, geologists delve deeper, employing sophisticated techniques such as electron microprobe analysis, X-ray diffraction, and Raman spectroscopy for a more comprehensive understanding of mineral composition.
Some minerals are instantly recognizable due to their unique features, while others require advanced scientific tools. In this guide, we’ll cover everything from preparing your mineral sample to selecting the right identification method. We’ll even explore the tools you can use at home for precise identification and offer tips on recognizing some of the most common minerals. Get your specimens ready – it’s time to unravel the mysteries of mineral identification!
If you are interested in checking out the best books about rock and mineral identification, you can find them here (Amazon link).
Create Your Mineral Identification Kit
A mineral identification kit is a geologist’s portable laboratory, a handy collection of tools for examining and identifying minerals in the field or at home. While pre-made kits are readily available online, it’s surprisingly simple to assemble your own.
Essentially, a mineral identification kit contains a selection of instruments for testing various mineral properties. Must-have tools include copper wire, a pocket knife, a piece of glass, and a quartz crystal for assessing hardness; a streak plate for determining streak color; dilute hydrochloric acid for testing for carbonates; a UV light for checking fluorescence; a magnet for assessing magnetism; and a hand lens for magnification.
- For hardness testing, non-mineral substitutes can be used to represent the various levels of the Mohs scale:
Copper Wire: With a hardness of approximately 3.5, copper wire is a versatile tool for assessing a mineral’s hardness. It can scratch softer minerals like talc, gypsum, and calcite but won’t leave a mark on harder minerals like fluorite.
Important Note: While some sources suggest using a copper penny or coin, it’s best to stick with copper wire. Coins are often made of copper alloys containing other metals, which can alter their hardness. Additionally, using copper wire provides a consistent standard across different regions and currencies.
- A pocket knife is another essential tool, but it doesn’t need to be fancy. In fact, an inexpensive knife is preferable, as overly hardened steel could skew your results. A typical pocket knife has a hardness of 5.5 to 6.5 on the Mohs scale, allowing you to test a range of minerals.
- A piece of glass is a simple yet valuable addition to your kit. A hardness of around 5.5 helps distinguish between minerals like apatite and orthoclase, which fall on either side of this hardness level.
- A small quartz crystal is a handy reference tool. Quartz is a common mineral, so finding an inexpensive, well-formed crystal shouldn’t be difficult. With a hardness of 7, it serves as a benchmark for determining whether a mineral sample is harder or softer than quartz on the Mohs scale.
- A streak plate. This tool is necessary for streak color identification. For example, it allows you to differentiate between gold and pyrite (fool’s gold). A streak plate can be any unglazed porcelain.
Tip! It is better to have a white and black streak plate for light and dark-colored minerals.
- Dilute HCl acid. This is the best tool for identifying calcite, as a reaction between acid and mineral produces bubbles. It allows you to differentiate between calcite and gypsum or calcite and halite quickly.
- A magnet. Iron-bearing minerals can be identified and differentiated with the help of a magnet. Magnetite (iron oxide with the highest iron concentration) can attract metal pieces, pyrrhotite can be attracted by a magnet, and hematite does not react to a magnet.
- UV light. It’s an essential tool if you are looking for fluorite, calcite, and scheelite (tungsten ore).
- A hand lens. A hand lens allows you to check the form (habit) of tiny crystals and identify them (for example, uvarovite garnet) or to check if faceted gemstones have any inclusions or fractures.
BTW: Do you want to know more about rock and mineral identification? The books listed below are the best ones you can find on the internet (Amazon links):
- Smithsonian Handbooks: Rocks & Minerals
- Gemstone & Crystal Properties (Quick Study Home)
- Ultimate Explorer Field Guide: Rocks and Minerals (National Geographic Kids)
Main Mineral Properties that Will Help You to Identify a Mineral
The mineral identification process is based on methodically checking the physical properties of minerals. The most significant advantage of these methods is that they can be easily held in the field, on mineral shows, or at home.
Mineral properties that are used for mineral identification are luster, hardness, color, transparency, streak, fracture, cleavage, specific gravity, magnetism, luminescence, reaction with hydrochloric acid, and morphology of crystals. Also, optical phenomena like birefringence and pleochroism can be tested.
So, let’s check out the physical properties of minerals:
Color and Any Other Visible Optical Effect
Color is the first obvious property that we notice. Minerals can occur in any color, hue, saturation, and tone. No additional tools are needed to identify a color. The sample should be clean and not weathered.
TIP: Rock color is the first property we pay attention to. Do you know why rocks have different colors? Find out the complete explanation in the article below:
Rock Colors: What Determines Color & Why Different Colors
Luster
No additional tools are needed for luster identification. Minerals have metallic and non-metallic (adamantine, glassy, matte, oily, waxy, mother-of-pearl, iridescent, and silky) luster.
Transparency
Transparency is the degree to which light is transmitted through a mineral. To differentiate between opaque, translucent, and transparent minerals, you may need a flashlight and a piece of printed text.
Streak
The streak is the color of the mineral in a powdered state. Sometimes, the color of the mineral sample and streak are different. This property can help you to identify some minerals very precisely. Use a streak plate or piece of unglazed porcelain for this test.
Cleavage and fracture
Cleavage is the ability of crystalline minerals to split along planes of weakness in the mineral’s structure, while fracture is a characteristic of the surface that is left after the splitting of a mineral.
No additional tool is needed to observe these properties if you don’t want to destroy your sample. However, if you want to initiate a fresh cleavage of fracture, you may need a hammer and chisel or a steel nail.
Hardness
Hardness is a resistance of minerals to scratching. A relative hardness scale used in mineralogy is the Mohs hardness scale. To determine the hardness, you can use your fingernail copper wire, a piece of glass, a pocket knife, and a quartz crystal, as we have discussed in the Create Your Mineral Identification Kit passage.
TIP: The advantage of the hardness test is that it can be easily done at home or even in the field while rockhounding. Check out the complete guide in the article below:
DIY Guide: Testing Mineral’s Hardness (Explained by Expert)
Specific Gravity
Specific gravity is the ratio between the mass (weight) of a mineral and the mass (weight) of an equal volume of water. In the field, it is determined only by weighing on the hand.
Magnetism, Luminescence, Reaction with Hydrochloric Acid
These properties are exotic, and very few minerals have them, but they are crucial for minerals like magnetite, fluorite, and calcite, respectively.
Professional Mineral Identification
Today, geologists use far more advanced methods to identify minerals. They mostly rely on chemical composition and crystal structure (atomic arrangement) rather than on physical properties.
Some methods are quick and non-destructive; others require powdering a part of a sample. Today, it is possible to make precise identifications of a few nanometers of minerals that are invisible to the naked eye.
Professional geologists and scientists use refractometers, polarization microscopes, electron microprobe analyzers, X-ray fluorescence, X-ray diffraction, Raman, and Infrared spectrometers to identify minerals on an advanced level. Sometimes, minerals should undergo a complicated sample preparation stage.
Sometimes, it is quite easy to identify a mineral just by looking at it. For example, violet crystals of amethyst are quite obvious. It is harder when minerals are cut and flawless. They lack any crystal faces, natural fracture surfaces, and inclusions.
Also, it is unacceptable to destroy even a small part of a stone. That is why non-destructive spectroscopic methods are so important for gemologists.
Nowadays, any new mineral can be found under huge magnification (with the help of an electron microscope). It is a great exception when a new mineral is found in macro sizes. But miracles happen! The new material comes mostly from remote areas in Africa.
TIP: Every professional geologist does it. Licking rocks and minerals in geology is a common practice to define some kind of minerals and, of course, a bunch of fun. Find out more in the article below:
Licking Rocks in Geology: Why & How (Answered by Geologist)
How to Prepare a Mineral for Identification
One of the most underestimated steps in mineral identification is sample preparation. That is why we decided to start with this stage, as many mistakes occur here.
We are going to discuss why it is important and how sample preparation differs for fresh minerals from the field, tumbled stones bought from mineral shows, faceted stones, and minerals that are going to be studied by scientists.
Before the identification of minerals, the sample should be checked and prepared. The studied sample should be carefully cleaned with water and dried. No weathered or altered surfaces should undergo testing of hardness and streak. Check if your sample is an individual crystal, mineral aggregate, or rock.
The most important rule for sample preparation is to clean the stone, whether it is just a freshly dug sample, tumbled opaque stone, or faceted sparkling gemstone.
You need to see a true color (not covered by clay from the earth or dust from a shelf) and luster. For example, dust can lower the stone’s luster from glassy to resinous or waxy.
It may seem obvious that freshly dug stone should be washed, but it is important to clean even faceted stone because the grease from hands left on the stone facets can distort refraction index measurements.
Mineral hunters need to pay attention to the freshness of the sample. Weathered surfaces have other physical properties: color is lighter, luster is more dull or absent, hardness is lower, and the fraction is earthy. The weathered surface should be removed. Physical properties should be tested on fresh surfaces only.
After cleaning the sample, observe it attentively. Try to respond to the next questions:
- Does it look like crystals with well-defined faces? For example, a prismatic quartz crystal or octahedral magnetite.
- Is it composed of one kind of mineral? Is it mineral aggregate? Like chalcedony, turquoise, or malachite.
- Is it composed of different minerals? If yes, it is a rock. Lapis lazuli is a rock composed of 3 different types of minerals (lazurite, pyrite, calcite). If you have a rock sample, pay attention to what mineral you are going to test for physical properties.
For rock hunters, it is very useful to pay attention to country rocks where the mineral is found. The type of country rock (sedimentary, metamorphic, or igneous) can narrow down possible candidates for identification.
For example, if you have found white transparent crystals between fractures of clay, it will hardly be colorless topaz as it tends to pegmatite bodies. Most probably, it is gypsum or calcite. Check hardness and reaction to hydrochloric acid, and your identification is completed!
TIP: The best way to identify the mineral is to consult with a specialist or with a rocks and minerals book. Check out the best book for Identifying Rocks & Minerals in the article below:
5 Best Books for Identifying Rocks & Minerals You Must Read
Step-by-Step Identification of Mineral
Let’s move to the identification. Follow the next 14 steps to identify your mineral sample. It’s going to be an interesting journey.
The most prominent way to identify minerals correctly is gradual and methodical testing of all physical properties. Check the essential ones first: hardness, luster, transparency, color, streak, cleavage, and fracture. Further, proceed with magnetism, luminescence, and morphology of crystals.
Step 1: Protection
During the mineral identification process, don’t forget to use gloves to protect your hand and something resistible, like a rubber mat or wooden board, to protect a surface where a test takes place. (tabletop or a floor).
Step 2: Choosing a Strategy
There are two approaches to mineral identification to narrow down possible candidates.
- The first one is based on luster (metallic or non-metallic). In most cases, the unknown sample will be placed into the sulfide or iron oxides group (metallic luster) or the silicate or halide group (non-metallic) luster.
- The second approach is based on hardness. An unknown mineral is tested by a piece of glass (5 on the Mohs scale) and then placed into a less than 5 hardness group or more than 5 hardness group.
These are just two possible options for the first step, and it doesn’t mean that in the case of luster identification, the hardness test should be omitted or vice versa. It’s just solving different tasks.
Step 3: Luster
No additional tools are needed to observe a luster. Metallic luster means a studied mineral belongs to the sulfide or iron oxides group. In the case of non-metallic luster, specify the type: adamantine, glassy, matte, oily, waxy, mother-of-pearl, iridescent, or silky.
Step 4: Hardness Identification (Scratch Test)
Hardness identification is one of the most important tests. It is based on a comparison of whether your mineral sample is harder or softer than a tool used for scratching (with an equivalent hardness to the Mohs scale standards).
To test the hardness of minerals, try to scratch a piece of glass. It allows you to understand whether your sample is harder or softer than 5 and gives you direction on how to choose the next tool.
Should it be copper wire or quartz crystal? This strategy lets you save some time and not move from the softest to the hardest tool or vice versa.
TIP: A scratch test is an essential method of mineral identification. It is widely used because of its simplicity. Check out the complete guide in the article below:
Performing Scratch Test on Rocks (Follow These 8 Steps)
Step 5: Color Identification
To identify the color of the mineral, start with the most obvious color and then add a shade. For example, blue -> greenish-blue for aquamarine.
In the cases with bicolor or polychrome minerals like tourmaline or ametrine, they indicate two colors.
Step 6: Transparency
Transparency is also a quite obvious characteristic. In order to differentiate between opaque and translucent minerals, you can try to watch the sun through the stone or use a flashlight. Minerals with metallic luster (Step 3) are opaque in most cases.
Please keep in mind that some minerals can appear transparent and opaque, depending on the mineral formation process and environment.
Step 7: Streak Test
Having completed the initial steps, you’ve gained valuable insights into the mineral’s luster and other properties. Now, the streak test can provide a crucial turning point, especially if the mineral exhibits a metallic luster.
The streak test involves rubbing the mineral against a streak plate (a piece of unglazed porcelain) to observe the color of the powder left behind. This is particularly useful for distinguishing minerals like pyrite (fool’s gold) from actual gold, as their streak colors differ significantly.
In fact, the streak test is a reliable method for identifying several metallic minerals, including sphalerite, galena, hematite, magnetite, and chromite, due to the often surprising difference between the mineral’s external color and its streak color.
This test is also important for minerals that occur in various colors. For instance, calcite and fluorite can be found in a multitude of hues, but their streak color will always be white, aiding in their identification.
While the streak test is a valuable tool, it’s not always applicable. If the mineral’s hardness exceeds 6 on the Mohs scale, attempting a streak test will likely only scratch the streak plate (which has a hardness of 5-5.5). In such cases, the streak test can be omitted, as it won’t provide accurate results.
TIP: Minerals’ streak is one of the most important tests for mineral identification, especially while working with native metals and sulfide minerals. Check out the complete guide in the article below:
DIY Guide: Testing Mineral’s Streak (Explained by Expert)
Step 8: Cleavage and Fracture
Observe your sample carefully. If it is a perfect undeformed crystal, there is no visible cleavage or fracture. At this stage, you have to decide if it is acceptable to destroy part of the sample or not.
If you can see distinct cleavage directions or fracture surfaces, try to classify them. Perfect, good, fair, poor for cleavage and granular, earthy, conchoidal, splintery, stepped, and uneven for fracture.
Cleavage is an important property for the identification of micas (biotite, muscovite, fuchsite). Conchoidal fracture, for instance, is typical for quartz.
Step 9: Specific Gravity
Specific gravity (SG) depends on the chemical composition and structure of the mineral. In the field, it is determined only by weighing on the hand. If a mineral feels light (like gypsum), its SG is around 2.5 g/cm3. Heavy minerals like galena have SG of more than 5 g/cm3
The medium SG is more common (from 2.5 to 5 g/cm3 and is typical for silicate minerals like quartz and feldspars.
Step 10: Magnetism, Luminescence, Reaction with Acid
At this stage, you can test and observe some non-typical properties like magnetism, luminescence, reaction with hydrochloric acid, and optical phenomena.
Checking of magnetism is needed if, in previous steps, the color of a mineral is indicated as black, luster is metallic and specific gravity is determined as heavy. Magnetism can help to differentiate between magnetite (which attracts a magnet) and hematite (which doesn’t interact with a magnet).
Luminescence can be tested with the help of UV light. Test your mineral in a dark room to obtain the best results. There is a list of minerals that glow under UV. The best examples are fluorite, calcite, corundum, scheelite, sodalite, and spodumene.
Reaction with hydrochloric acid can help you to identify calcite easily. After placing a few drops of dilute hydrochloric acid (HCl) on a surface of calcite, you will observe bubbles.
TIP: Minerals and rocks can completely change their colors by being subjected to UV light or black light. Check out the most common rocks and minerals that glow under UV light:
12 Rocks & Minerals That Glow Under UV Light & Black Light
Step 11: Optical Phenomena
Observe a sample carefully to see if it has a cat’s eye effect (typical for quartz, chrysoberyl, apatite), asterism (common for rubies and sapphires), does it have pleochroism (tourmalines, tanzanite, iolite), color change effect (alexandrite), or birefringence (calcite, zircon).
These optical phenomena can help you to identify a mineral sample.
Check 23 Main Properties of Rocks & Minerals Explained by Experts to see more minerals that have optical phenomena.
Step 12: Crystal Shape (Habit)
If your mineral sample has some even crystal faces or is a well-formed crystal, observe it attentively. Crystal habit can tell you the mineral species:
- Cubic form is typical for fluorite and pyrite
- Octahedron – for spinel, diamond, magnetite, and fluorite.
- Dodecahedron – for garnets
- Rhombohedral (tilted cube) and scalenohedron are typical for calcite
- Hexagonal – typical for beryls (emerald, aquamarine, heliodor)
Step 13: Mineral associations
Sometimes, mineral associations can be a game-changer. For example, lazurite and azurite are both blue minerals that usually occur as aggregates. Lazurite usually occurs together with golden specks of pyrite and white crystals of calcite, while azurite is commonly associated with malachite.
Step 14: Results
All these steps will help you to identify minerals or at least narrow down possible candidates and decide on a group of minerals (oxides, sulfides, halides, silicates).
You can use the next resources to compare your obtained results and observations with tables of possible mineral candidates:
TIP: Do you know the difference between precious and semi-precious stones? Precious and semi-precious stone terms are surrounded by feelings of beauty, brilliance, and wealth. Find out more in the article below:
Precious & Semi-Precious Gemstones: Explanation & Difference
Bonus! The Most Common Minerals Identification Tips
Here is a table with a list of very common minerals and their typical characteristics, which help to identify a sample quickly.
For example, pyrite’s unique properties that differ from any other minerals are metallic luster, greenish-black streak, and cubic shape of crystals.
| Mineral | Typical Characteristics |
|---|---|
| Quartz | Hardness: 7 Crystal Shape: Hexagonal prism with pyramid |
| Mica | Cleavage: Perfect mineral peels when rubbed Crystal Shape: Flakes |
| Pyrite | Luster: Metallic Streak: Greenish-black Crystal Shape: Cubic |
| Gypsum | Hardness: Can be scratched by a fingernail |
| Calcite | Cleavage: Perfect in three directions Luminescence: Glow under UV light Crystal Shape: Rhombohedral (tilted cube) |
| Fluorite | Luminescence: Glow under UV light Crystal Shape: Cubic Octahedron |
| Magnetite | Luster: Metallic Streak: Black Magnetism: Attracts a magnet Crystal Shape: Octahedron |
| Hematite | Luster: Metallic Streak: Red |
| Galenite | Luster: Metallic Specific Gravity: Heavy Streak: Gray |
| Lazurite | Mineral Association: In association with calcite and pyrite |
| Azurite | Mineral Association: In association with malachite |
Conclusion
Identifying minerals with the step-by-step instructions discussed is easy and amusing. The approach is based on:
- testing the physical properties,
- the morphology of crystals,
- and minerals association.
Hardness, luster, cleavage, color, transparency, streak, fracture, and specific gravity are the main physical properties for mineral identification in the field or at home.
Optical phenomena, magnetism, luminescence, and reaction with acid can also come in handy with some kinds of crystals.
Note: This article is written by gemologist expert Olena (LinkedIn profile). She is a Ph.D. candidate (Mineralogy) holding an Applied Jewelry Professional diploma from GIA (Gemological Institute of America).
TIP: So you already know how to identify minerals. What about starting to find minerals on your own? Check out the ultimate guide on starting rockhounding in the article below:
How to Start Rockhounding: The Ultimate Beginner’s Guide