Mineral
Phlogopite
KMg₃(AlSi₃O₁₀)(F,OH)₂Flogopit
A magnesium mica whose name means “fire-like”: it resists heat and can form crystals up to 10 metres long.
Also known as: Magnesium mica
- Popularly: Ore and raw material
- Industrial
- Important in Türkiye
In short
Phlogopite is the magnesium end of the mica family. It forms a series with biotite: as iron increases, phlogopite passes into biotite. It is reddish brown, yellowish brown, green or white; it splits into thin sheets, and these sheets are flexible and elastic. It occurs in magnesium-rich rocks, that is, in dolomitic marbles, in ultramafic rocks such as kimberlite and in skarns.
Photos
How does it form?
Phlogopite is the mica of magnesium-rich settings. It crystallises in the contact zones where a magma heats the surrounding rocks, in marbles formed by the transformation of dolomitic limestones, and in skarns. It also occurs in ultramafic rocks such as kimberlite, lamproite and peridotite, and in serpentinites. In some deposits it forms crystals measured in metres.
What is it used for?
- Insulating mica: The uses of phlogopite are similar to those of muscovite: because it resists heat and does not conduct electricity, it is used in sheet and ground form for heat and electrical insulation (see the Muscovite page).
- Synthetic mica: According to the U.S. Geological Survey (USGS), where thermal and electrical properties are needed, synthetic fluorophlogopite can take the place of ground natural mica.
- Collecting: Large hexagonal plates and well-formed crystals find a place in mineral collections.
One end of the biotite series
Phlogopite is the magnesium end of the biotite series. The iron-rich end of the series is annite, and the dark micas in between are mostly called “biotite” (see the Biotite page).
In Türkiye
In the Black Sea region, in the Camiboğazı skarn in the Gümüşhane area, well-crystallised phlogopite, vesuvianite and diopside occur where the Eocene Zigana Granitoid meets dolomitic limestone.
What determines its value?
The industrial value of phlogopite depends on the size, flatness, freedom from stains and purity of the sheets: large, flat, clean sheets are sought as insulators, while crushed (scrap and flake) mica is sold by the tonne as an inexpensive filler. Collectors give a small value to large, regular hexagonal plates and well-formed crystals, especially from famous localities.
This information is educational, not buying, selling or investment advice. Value varies enormously with quality and treatment.
How to recognise it
- 1
Reddish brown, yellowish brown, sometimes green or white, shining plates; the crystals are six-sided, thick and tabular, and often taper towards the end.
- 2
It is very soft (hardness 2–3): a fingernail or a copper coin can scratch it. Its thin sheets are flexible and spring back when bent and released.
- 3
It is told from biotite (the nearly black dark mica) by colour: because of its low iron, phlogopite is lighter, reddish or yellowish brown. As the two form a series, there is no sharp boundary between them.
- 4
In carbonate rocks such as marble and dolomite it occurs with diopside, calcite, dolomite, apatite and vesuvianite; in magnesium-rich rocks such as kimberlite and peridotite, with olivine.
Fakes and imitations
What shops usually don’t tell you:
- Shining yellowish-brown mica flakes in river sand or in rock can be mistaken for gold. Mica is light and splits into leaves under a needle point; gold is heavy and flattens when pressed.
Myths and misconceptions
MythThe yellowish flakes that sparkle in the sun in a river bed are gold.
FactMost of these flakes are mica; micas such as phlogopite and biotite can weather to a yellowish or bronze colour. Gold is very heavy and sinks at once in a pan; mica flakes are light, are easily carried off by water and, when pressed with a needle, split into leaves instead of flattening.
MythPhlogopite and biotite are two independent, separate minerals.
FactPhlogopite is the magnesium end of the biotite series; as iron increases, the series passes towards the iron-rich end of biotite. The dark micas in between are mostly called “biotite”, and which end they are closer to can only be settled by chemical analysis.
Did you know?
Its name comes from the Greek for “fire-like” and points to the reddish colour phlogopite often shows.
The largest known single phlogopite crystal was found at the Lacey mine in Canada: it measured about 10 × 4.3 × 4.3 metres and, according to sources, weighed 270–330 tonnes.
Where is it found?
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- Lacey mine, Loughborough, Frontenac County, Ontario, Canada · Major depositCanada's largest phlogopite mica mine; the largest known single phlogopite crystal was found here (about 10 × 4.3 × 4.3 m)
- Slyudyanka, near Lake Baikal, Russia · Known locality
- Franklin, Sussex County, New Jersey, USA · Known locality
- Campolungo, Ticino, Switzerland · Known locality
- Fassa Valley, Trentino-Alto Adige, Italy · Known locality
- Camiboğazı skarn deposit, Gümüşhane, Türkiye · Known localityWell-crystallised phlogopite in skarn at the contact of the Zigana Granitoid with dolomitic limestone; the point marks the Gümüşhane area
Locations are approximate to protect sites. Red dots mark places in Türkiye. Open in the big map →
Frequently asked questions
What is phlogopite?
Phlogopite is the magnesium end of the mica family. It forms a series with biotite: as iron increases, phlogopite passes into biotite. It is reddish brown, yellowish brown, green or white; it splits into thin sheets, and these sheets are flexible and elastic. It occurs in magnesium-rich rocks, that is, in dolomitic marbles, in ultramafic rocks such as kimberlite and in skarns.
What is phlogopite used for?
Insulating mica: The uses of phlogopite are similar to those of muscovite: because it resists heat and does not conduct electricity, it is used in sheet and ground form for heat and electrical insulation (see the Muscovite page). Synthetic mica: According to the U.S. Geological Survey (USGS), where thermal and electrical properties are needed, synthetic fluorophlogopite can take the place of ground natural mica. Collecting: Large hexagonal plates and well-formed crystals find a place in mineral collections.
How hard is phlogopite?
It has a hardness of 2–3 on the Mohs scale. A fingernail cannot scratch it, but a steel knife can. Its specific gravity is 2.78–2.85 g/cm³.
Where is phlogopite found?
Its best-known localities: Lacey mine, Loughborough, Frontenac County, Ontario, Canada; Slyudyanka, near Lake Baikal, Russia; Franklin, Sussex County, New Jersey, USA; Campolungo, Ticino, Switzerland; Fassa Valley, Trentino-Alto Adige, Italy.
Where is phlogopite found in Türkiye?
Known localities in Türkiye: Camiboğazı skarn deposit, Gümüşhane, Türkiye.
How can you tell if phlogopite is real?
Reddish brown, yellowish brown, sometimes green or white, shining plates; the crystals are six-sided, thick and tabular, and often taper towards the end. It is very soft (hardness 2–3): a fingernail or a copper coin can scratch it. Its thin sheets are flexible and spring back when bent and released. It is told from biotite (the nearly black dark mica) by colour: because of its low iron, phlogopite is lighter, reddish or yellowish brown. As the two form a series, there is no sharp boundary between them. Shining yellowish-brown mica flakes in river sand or in rock can be mistaken for gold. Mica is light and splits into leaves under a needle point; gold is heavy and flattens when pressed.
Is phlogopite valuable?
On the “street to diamond” value ladder it sits on step 3 of nine: Building and industrial stone. The industrial value of phlogopite depends on the size, flatness, freedom from stains and purity of the sheets: large, flat, clean sheets are sought as insulators, while crushed (scrap and flake) mica is sold by the tonne as an inexpensive filler. Collectors give a small value to large, regular hexagonal plates and well-formed crystals, especially from famous localities.
Sources
- Handbook of Mineralogy: Phlogopite · Mineralogical Society of America
- Phlogopite · Webmineral
- Phlogopite · Wikipedia
- Mineral Commodity Summaries 2026: Mica (Natural) · U.S. Geological Survey, 2026
- Ontario Mineral Inventory: Lacey (Loughborough Township) · Ontario Geological Survey
- Formation of skarns at Gümüşhane (Northeastern Turkey) (Sipahi), Neues Jahrbuch für Mineralogie – Abhandlungen 188(2) · E. Schweizerbart, 2011
External links
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