Fayalite is the iron-rich end member of the olivine solid solution series and is typically found in high-silica volcanic rocks and certain granitic environments. It is noted for its high density and tendency to oxidize into hematite or magnetite when exposed to air. Collectors look for dark, well-formed crystals often embedded in light-colored volcanic matrix.

Hardness

6.5-7

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineraluncommonOlivine Group family

Fayalite

Hardness: 6.5-7
Luster: Vitreous
Streak: White
Transparency: Translucent

Is this fayalite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch fayalite with a known reference. Fayalite sits at Mohs 6.5-7 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Fayalite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Fayalite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: yellow, yellow-green, brown, black.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: prismatic crystals, massive, granular.

Often confused with

Fayalite vs. its common look-alikes — and how to tell them apart in the field.

Often found alongside fayalite

Minerals reported to co-occur with fayalite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: Fe₂SiO₄
Mohs hardness: 6.5-7
Density: 4.39 g/cm³
Colors: Yellow Yellow-green Brown Black
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Orthorhombic
Crystal habit: Prismatic Crystals, Massive, Granular
Cleavage: Poor in Two Directions
Rarity: Uncommon
Uses: Collector, Scientific Research
Host rock: Igneous Rocks Such as Rhyolites, Granites, And Iron-rich Basaltic Rocks
Typical price: $10-50 per specimen depending on crystal quality

Where rockhounds find fayalite

Classic worldwide localities

Mourne Mountains, Ireland
Rockport, Massachusetts, USA
Jan Mayen Island, Norway
Pantelleria, Italy

Field-hunting tip

Look in igneous rocks such as rhyolites, granites, and iron-rich basaltic rocks country — that is the host setting where fayalite typically forms. If you start seeing quartz, tridymite, magnetite in float, you are in the right ground. Field specimens usually show a prismatic crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify fayalite?+

Mohs hardness is 6.5-7. It typically shows a vitreous luster. The streak is white. Common colors include yellow, yellow-green, brown, black.

Where is fayalite found?+

Notable localities include Mourne Mountains, Ireland; Rockport, Massachusetts, USA; Jan Mayen Island, Norway; Pantelleria, Italy.

How much is fayalite worth?+

Typical asking prices fall in the range of $10-50 per specimen depending on crystal quality. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like fayalite?+

Fayalite is most often confused with Forsterite, Tephroite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with fayalite?+

Fayalite commonly co-occurs with Quartz, Tridymite, Magnetite, Ilmenite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does fayalite form in?+

Fayalite typically forms in igneous rocks such as rhyolites, granites, and iron-rich basaltic rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is fayalite used for?+

Fayalite is used in collector, scientific research.

Find fayalite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.