Seidite-(Ce) is an extremely rare silicate mineral characterized by its thin, fragile tabular crystal habit and yellow-to-brown coloration. It is primarily found as an accessory mineral in complex agpaitic alkaline pegmatites, most notably within the Khibiny Massif in Russia. Collectors prize it for its unique chemical structure, though its rarity makes high-quality display specimens difficult to acquire.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineralrare

Seidite-(Ce)

Hardness: 3
Luster: Vitreous
Streak: White
Transparency: Translucent

Is this seidite-(ce)?

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 seidite-(ce) with a known reference. Seidite-(Ce) sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Seidite-(Ce) leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Seidite-(Ce) typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: yellow, brown.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: thin tabular crystals.

Often confused with

Seidite-(Ce) vs. its common look-alikes — and how to tell them apart in the field.

mineral

Nenadkevichite

Mohs 5

How to tell apart: Nenadkevichite is the harder of the two (Mohs 5 vs. 3).

Compare →

Often found alongside seidite-(ce)

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

All properties

Chemical formula: Na₄Ce₂TiSi₈O₂₂·5H₂O
Mohs hardness: 3
Density: 2.8 g/cm³
Colors: Yellow Brown
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Thin Tabular Crystals
Cleavage: Perfect in One Direction
Rarity: Rare
Uses: Collector
Host rock: Agpaitic Pegmatites
Typical price: $50-300 per specimen

Where rockhounds find seidite-(ce)

Classic worldwide localities

Khibiny Massif, Kola Peninsula, Russia

Field-hunting tip

Look in agpaitic pegmatites country — that is the host setting where seidite-(ce) typically forms. If you start seeing microcline, aegirine, nepheline in float, you are in the right ground. Field specimens usually show a thin tabular crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify seidite-(ce)?+

Mohs hardness is 3. It typically shows a vitreous luster. The streak is white. Common colors include yellow, brown.

Where is seidite-(ce) found?+

Notable localities include Khibiny Massif, Kola Peninsula, Russia.

How much is seidite-(ce) worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like seidite-(ce)?+

Seidite-(Ce) is most often confused with Nenadkevichite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with seidite-(ce)?+

Seidite-(Ce) commonly co-occurs with Microcline, Aegirine, Nepheline, Eudialyte. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does seidite-(ce) form in?+

Seidite-(Ce) typically forms in agpaitic pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is seidite-(ce) used for?+

Seidite-(Ce) is used in collector.

Find seidite-(ce) on the map

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