Identifying Minerals in Rocks: A Comprehensive Guide


Mineral Identification and classification

Mining and Exploration

Geology Handbook

Discovering the World Beneath Your Feet

Every rock has a story to tell, and understanding the minerals that make up these rocks can provide valuable information about the environment and geological processes that formed them. In this article, we will dive into the fascinating world of minerals and explore how to identify them in rocks, their nutrient value, and where to find them.

What are Minerals?

The Building Blocks of Rocks

Minerals are naturally occurring, inorganic substances with a specific chemical composition and crystalline structure. They are the essential building blocks of rocks and significantly shape our planet’s surface and deep interior. There are over 5,000 known minerals, but only a few dozen are considered common and make up the majority of Earth’s crust.

Identifying Minerals in Rocks

A Step-By-Step Guide

Observe Color

While only sometimes the most reliable identifier, colour can be a useful starting point. Some minerals, like quartz and feldspar, come in various colours, while others, such as malachite and azurite, have distinctive hues.

Examine Luster

Luster refers to the way a mineral reflects light. There are two main categories: metallic (shiny and reflective, like metal) and non-metallic (dull, glassy, or earthy). Identifying a mineral’s lustre can help narrow down your options.

Determine Hardness

Hardness is a measure of a mineral’s resistance to scratching. The Mohs scale ranks minerals from 1 (talc, the softest) to 10 (diamond, the hardest). You can perform a simple scratch test using your fingernail, a steel nail, or a glass plate to get a rough estimate of a mineral’s hardness.

Check for Cleavage or Fracture

Cleavage refers to how a mineral breaks along specific planes, while fracture describes an irregular break. Observing these properties can help distinguish between minerals with similar appearances.

Assess Streak

The streak of a mineral is the colour of its powdered form. To test this, drag the mineral across an unglazed porcelain tile (streak plate) and observe the colour left behind.

Where to Find Minerals

Exploring the Great Outdoors

The best way to discover minerals is to explore different geological environments. Sedimentary rocks, such as limestone and shale, often contain fossils and unique minerals like calcite and pyrite. Igneous rocks, like granite and basalt, are home to quartz, feldspar, and mica. Metamorphic rocks, such as marble and schist, can host garnet, staurolite, and other fascinating minerals. Keep an eye out for outcrops, road cuts, or quarries, as these are often excellent places to find exposed rocks containing various minerals.

Stay Safe and Respect the Environment

When searching for minerals, always follow safety guidelines and practice responsible collecting. Wear appropriate gear, like sturdy shoes and gloves, and be mindful of your surroundings. Obtain permission to collect on private property and adhere to any regulations in protected areas. Lastly, be respectful of the environment and minimize your impact while exploring.

Mineral varieties can vary by small amounts of impurities. 

Amethyst is a purple variety of Quartz

Classification: Large Crystals or small crystals?


The individual crystal size of all rocks cooling from magma or lava is a direct result of how much time they have to grow. The longer a mineral has to grow, the larger the crystals will be. This means the speed at which molten rock solidifies directly determines the size of the crystals.

So for a given magma composition, there will be an extrusive and an intrusive version, Chemically identical to each other. Basalt is the extrusive (from lava flows) version of Gabbro. Rhyolite is the extrusive version of Granite.

And just to get confusing, some magmas may cool quickly at one point, but slowly at another (two stage cooling) which will result in some large crystals in a mostly small crystal rock. These rocks and their texture are classified as porphyritic.

A magma that has millions of years to cool deep in the earth will tend to form/grow large easily distinguishable crystals. A magma (or lava at the earth’s surface) which explodes into air or water and cools very quickly will only have very tiny crystals – so small you may need magnification to see them.

Fractional crystallization.

There are also rocks where some crystals form and sink to the bottom of the magma, then another, and another… forming layers. This is especially important to the formation of chromite deposits.


Get In Touch provides general information on geology, mining, and exploration in Canada and is not intended as professional advice. Users should consult qualified professionals before making decisions based on site content. While we strive for accuracy, we cannot guarantee error-free, complete, or current information and assume no responsibility for discrepancies. We are not liable for damages from using or relying on-site content, and users indemnify and its affiliates from claims arising from their use. External links are not endorsed, and this disclaimer may change without notice. Continued use signifies acceptance of changes. participates in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to,, and affiliated sites. As an Amazon Associate, we earn from qualifying purchases through our links.