Epidote vs Diopside: What Are They, And What's The Difference?

If you were wondering what the difference between Epidote and Diopside was, then this article is for you.

Even if you simply want more information about either mineral, then you have come to the right place.

Let’s take a closer look at these two similar minerals.

Epidote vs Diopside: EXPLAINED

What is Epidote?

The word “Epidote” is used in mineralogy in two ways:

The “Epidote Group” belongs to a collection of silicate minerals with similar structural and compositional features, and

“Epidote” refers to the most frequent mineral in the Epidote Group.

As a mineral, Epidote is a silicate that is typically found in low- to moderate-grade regionally metamorphosed rocks.

Epidote is often found in these rocks alongside amphiboles, quartz, feldspars, and chlorite.

It may be found as substitutes for mineral grains which have undergone metamorphism. It’s often found in granite veins that cut through the rock.

In pegmatites, they appear as monoclinic crystals.

It may also be found in marbles and schists that have undergone contact metamorphism as monoclinic crystals in massive form.

The hue of epidote varies from pistachio green to yellowish-green.

Black to brownish green is less common.

It is normally transparent and has a vitreous shine in huge form.

Marble and pegmatite crystals with well-formed crystals are often translucent.

Ca2(Al2,Fe)(SiO4)(Si2O7)O is the chemical formula for epidote (OH).

It’s the last member in a crystalline series that also includes clinozoisite.

As a mineral, the crystal structure of representatives of the epidote family is made up of solitary and coupled silica tetrahedrons.

They have the chemical formula A2M3(Si2O7)(SiO4)O in common (OH).

Calcium, strontium, manganese, lead, or rare-earth elements make up the letter “A”

Aluminum is commonly combined alongside iron, manganese, magnesium, or vanadium as “M”

The chemical compositions of some of the epidote group’s constituent minerals.

What is Diopside?

MgCaSi2O6 is the chemical formula for diopside, a rock-forming pyroxene mineral.

It may be found in metamorphic and igneous rocks all over the globe.

Diopside crystals of gem grade are faceted into beautiful gemstones that are sometimes used in commercial jewelry.

Granular diopside may be readily chopped and polished. It is occasionally used as a decorative stone since it has a pleasing hue.

The importance of diopside as an indication mineral in the quest for diamonds is perhaps its most significant application.

Diamond deposits have been discovered utilizing trail-to-lode prospecting techniques employing diopside as well as other indicator minerals in Canada, Africa, the United States, and other regions.

Diopside offers potential use in the ceramics and glass industries, but it is generally found in tiny, impure deposits that are difficult to mine.

Are There Similarities between Diopside and Epidote?

In terms of crystals, Diopside and Epidote are both Monoclinic and prismatic crystals.

Both were named by Rene Just Haüy in the 19th century.

That is the basics of what these two minerals have in common.

They differ in all other areas.

What are the Differences Between Diopside and Epidote?

Firstly, their chemical compositions are different. Epidote is Ca₂Fe³⁺_2.25Al_0.75(SiO₄)₃(OH) while that of Diopside is CaMgSi2O6.

The molecular weight of Epidote is also much higher than that of Diopside at 519.3 grams versus 216.55 grams.

Epidote is almost a quarter iron (Fe) and is followed by silicon (Si) and calcium (Ca) at 15.44% and 16.22%.

Diopside, on the other hand, is quarter silicon, 18.51% calcium, and 11.22$ magnesium.

Epidote can be found in contact with metamorphic rocks, while diopside is found in basic and ultrabasic igneous and metamorphic rocks.

Their occurrence is also different and one of the best clues as to which of the two stones you have discovered.

Only Igneous rocks contain epidote, whereas diopside can be found in Ca-rich metamorphic rocks; in kimberlite.

Diopside is also more widely found across the globe from Burma and Madagascar to Russia and Finland.

In all these areas, its color differs according to which area it is found in.

The two minerals also differ in color.

Epidote is yellowish-green, brownish-green, and black, yellow, gray while that of diopside is blue, brown, colorless, green, or gray.

Their density is almost the same with epidote at an average of 3.45 and diopside at 3.4.

Their diaphaneity is also almost the same, yet different.

Epidote is transparent to translucent, to opaque, while diopside can be described in the same way, but is not opaque.

Diopside is also more brittle than epidote with a hardness of 6 (orthoclase) while epidote has a hardness of 7 (quartz).

Diopside can have a blue or purple fluorescence, while epidote is not fluorescent at all.

Minerals associated with epidote are aegirine, allanite, calcite, fluorite, grossular, microcline, prehnite, pyrrhotite, and titanite are some of the minerals found in aegirine, while diopside is associated with arfvedsonite, calcite, and pectolite.

Another difference between the two minerals is that epidote is heat sensitive while diopside is not heat sensitive.

Epidote will therefore show physical changes and heat up quicker when exposed to heat, whereas, diopside will not.

Whereas Epidote has perfect cleavage, diopside is less perfect and is described as good.

Why are Epidote and Diopside confused with each other?

These two minerals are confused because they look rather similar.

It takes someone with experience to tell them apart.

Most people can tell them apart easily when they have a specimen of both, but the problem is knowing what you have when you only have access to a single specimen.

To make the task more difficult, their basic structure is also very similar.

One of the easiest ways of telling them apart is to check for fluorescence, but diopside is not always fluorescent.

If the stone is slightly florescent, you know it is diopside.