High Density Rocks Examples (Characteristics and Types)

In this article, you’ll get to know some commonly known high density rocks, as well as information about high density rocks to better understand them.

High Density Rocks Examples (Characteristics and Types)

What are high density rocks?

When talking about high density rocks, we are discussing the specific gravity of the rock, which is determined by measuring its mass versus the density of water.

This may sound fairly complex, but it’s actually not all that complex at all.

Measuring the density of any substance comes down to the amount of mass per unit of measure it has and dividing by its volume.

Water density is used as a baseline for specific gravity measurements of substances and has a density rating of 1 g/cm3 (one gram per cubic centimetre).

Therefore, to get the specific gravity of a substance, you take the density of the substance and compare it to the same water measurement.

If a substance has a lower gravity rating than water, it will float.

What are some factors that can affect rock density?

There are several factors that can affect the density of a substance which is worth being familiar with as well.

Mineral Composition

The first of these is material composition, which has an impact on all rock types.

Most of the common rock types contain silica minerals, which are abundant rock-forming minerals.

Because of this, we need to look at the other elements (such as iron, magnesium, aluminum etc.) present in any rock in order to get its specific density.

The density of different rock types therefore decreases with the higher amounts of silicates present in the material making up the rock’s whole.

Igneous rocks, for example, have multiple classifications; mafic, ultramafic, felsic and intermediate.

These classifications make it easier to determine where certain minerals may be found, as denser materials tend to rest deeper in the earth etc.

Here is a break down of the igneous rock classifications:

  • Mafic – igneous rocks consisting of more heavy mineral elements such as iron and magnesium than silicate material
  • Ultramafic – igneous rocks primarily consisting of heavy mineral elements and little silicate material
  • Felsic – igneous rocks consisting of higher amounts of silicates (feldspar and quartz) and fewer heavy metals
  • Intermediate – igneous rocks consisting of roughly equal amounts of silica and heavy mineral elements

Understanding mineral composition and density classification helps us explain the various layers of earth’s crust and why they exist where they do.

Sedimentary and metamorphic rocks are much more difficult to classify.

The density of sedimentary rocks is dependent on the parent material, which varies greatly, and the density of metamorphic rocks is dependent on both the parent material and the transformation it has gone through.


The second factor that can affect the density of a substance is the porosity of the rock, which is determined by the amount of void space between its mineral grains.

Here are two different commonly used calculations to determine porosity:

  • (Porosity = total voids / total volume) x 100%
  • Porosity = ((total volume – volume of the solid) / total volume) x 100%

Rocks with interlocking minerals, like granite, tend to have low porosity (below 1%).

Rocks with independent mineral grains, like sandstone, tend to have high porosity (upwards of 35%).

The porosity of sandstone is extremely useful for geologists that are trying to locate oil reserves as the void space in sandstone acts like a sponge, trapping the oil in between its mineral grains.


Lastly, let’s briefly touch on pressure.

As sedimentary rocks are exposed to periods of extreme pressure, the materials in the rock are compressed, reducing the void space between the mineral grains.

The result of this is a much denser rock.

Again, this helps us better understand the various layers in the earth’s crust and how and when they may have formed.

What are some examples of high density rocks?


Olivine is a rock forming mineral which is relatively common in mafic and ultramafic rocks like gabbro, peridotite and basalt.

Olivine tends to be olive green in color, but it can also appear brownish or green with yellow highlights.

Most people know olivine as its gemstone quality version, peridot.

It has a glassy appearance that is either transparent or translucent.

Olivine is most commonly found in igneous rocks near areas where tectonic movement has pushed the material to the surface as it forms at a very high temperature and these materials come from deep in the earth.

Olivine crystals can also sometimes form in dolomite and limestone during metamorphism.

When olivine goes through a metamorphic process, it becomes serpentine.

Common commercial applications for olivine include metallurgy (slag conditioner) and jewellery making.

Olivine has a specific gravity rating of between 3.2 and 4.4.


Galena is the primary source of lead and is mined extensively around the world but has little other commercial use.

Lead is primarily used in the making of vehicle batteries and backup batteries for computer networks these days, as most other uses have disappeared due to health concerns regarding its use in things like paint, plumbing, bullets, fishing weights, glazes, cosmetics, plastics, fuel, glass and more.

Galena forms as veins in igneous, metamorphic and sedimentary rocks.

You can identify galena quite easily in the field by its perfect cleavage that goes in three directions, intersecting at 90 degree angles, and a bright, silvery lustre.

Another identifier is how it tarnishes to a dull grey. It will produce a dark grey streak when rubbed against a rough surface and is quite heavy.

Galena is also important to prospectors as it can contain silver.

Samples containing silver tend to have a more curved cleavage as the silver content disrupts the structure of the galena crystals.

Galena can be smelted very easily at lower temperatures than most metals and you can even extract lead from a sample by placing it in a campfire and collecting the lead from the bottom of the firepit after the fire has burnt out.

Galena has a specific gravity rating of between 7.4 and 7.6 due to its lead content.


Hematite is an iron oxide that is a common rock forming mineral in igneous, sedimentary, and metamorphic rocks.

Of all the iron-rich ores, it is the most important because of its abundance and, for this reason, it is mined extensively wherever significant deposits are found.

While there are other commercial uses for hematite, the economic value is considered small in comparison with iron.

It is used to make radiation shielding, ballast, pigments and other products.

The most common way to identify hematite is the reddish streak that it leaves when rubbed against a rough surface.

It can appear red, black, grey, brown and silver in color and typically has an earthy to metallic luster.

Another method is to use a magnet to check the sample. If the magnet does not react, it is most likely hematite as it is not magnetic.

If the magnet does react, then the sample most likely contains large amounts of magnetite.

Hematite has a specific gravity rating of between 5.0 and 5.3.

High Density Rocks Examples