Mineral Collector Glossary: Thumbnail, Cabinet, Matrix, Float, Pseudomorph, and More

Mineral collecting uses shorthand that can be confusing to new buyers. Terms such as thumbnail, miniature, cabinet, matrix, float, contact, termination, pseudomorph, and ex-collection describe size, formation, condition, or history—not metaphysical quality. Definitions also vary between dealers and collector communities, so exact measurements and clear photographs should override shorthand.

Specimen size terms are approximate

Mineral-size categories developed as convenient collecting and display terms, but there is no single universal standard used by every seller, show, museum, or competition. One dealer’s miniature may overlap another seller’s small cabinet specimen.

Never purchase from the size word alone. A three-dimensional specimen can fit one measurement while extending much farther in another direction.

Micromount

A micromount is a small mineral specimen prepared for viewing under magnification, often in a small protective box. Micromounts can preserve exceptional crystals too small to appreciate with the unaided eye. Small size does not imply low scientific or collector interest.

Thumbnail

A thumbnail is a compact specimen commonly displayed in a small box. Collectors often value thumbnails because the crystal, matrix, and overall composition can be complete at a manageable size. The term describes scale, not quality.

Miniature, small cabinet, and cabinet

These terms indicate increasingly larger specimens. They help collectors plan cases, boxes, and budgets, but exact definitions differ. A cabinet specimen may require a strong shelf, stable stand, and more careful transport. Ask for dimensions and weight before buying.

Perky box

A Perky box is a small clear plastic display box, commonly used for thumbnail-sized specimens, with a removable base and mounting material. The brand name is sometimes used generically. Mounting putty, adhesive, or mineral tack should be disclosed when it affects the specimen.

Matrix

Matrix is the host rock or material on which crystals formed or remain attached. Matrix can provide geological context, associated minerals, contrast, and stability. It can also be fragile, unattractive, artificially trimmed, repaired, or partly reconstructed.

A specimen described as “on matrix” should show how the crystals connect to the host. The base photograph is important.

Association

An association specimen contains two or more mineral species occurring together. The combination may be common or unusually important because of locality, crystal quality, or geological relationship. A seller should distinguish confirmed associated minerals from visual guesses.

Float specimen

A float is a crystal or specimen believed to have formed without a normal attachment point, often showing crystal faces around much of its surface. In practice, the word may be used loosely. Inspect for contacts, broken attachment areas, trimming, repairs, and artificial bases.

Contact

A contact is an area where a crystal grew against another crystal, matrix, or surrounding material, preventing a free face from developing. Contacts are natural features and are not the same as fresh damage. Their effect on value depends on placement, visibility, and the specimen’s overall quality.

Termination

A termination is the natural end of a crystal where faces close the crystal form. A crystal can be singly terminated, doubly terminated, incomplete, contacted, or broken. A polished point is not a natural termination.

Crystal habit

Habit describes the characteristic external form in which a mineral grows, such as prismatic, tabular, acicular, bladed, fibrous, dendritic, or botryoidal. Habit can help identification, but it is not sufficient by itself.

See Natural Crystal Habit vs. Carved Shape for a full comparison.

Vug and pocket

A vug is a cavity in rock lined with crystals or mineral material. A pocket is a mineral-filled cavity encountered during mining or collecting. Dealers may describe a specimen as a “pocket piece” when it came from a documented find. Pocket claims are strongest when supported by mine records or reliable provenance.

Druzy or drusy

Druzy describes a surface covered by many small crystals. Both spellings appear in the trade. Druzy surfaces can sparkle strongly but may be delicate, coated, dyed, or attached to a different host material.

Botryoidal

Botryoidal material has rounded, grape-like forms produced by mineral growth. The term describes shape, not a species. Hematite, chalcedony, malachite, and other minerals can form botryoidal surfaces.

Stalactitic

Stalactitic mineral growth forms elongated, hanging or tube-like structures, often with concentric internal layers. A broken cross-section may reveal banding. Not every elongated specimen is a stalactite.

Pseudomorph

A pseudomorph is a mineral that has replaced or altered from another mineral while preserving the external form of the original. The name usually identifies the present mineral after the original, such as “goethite after pyrite.” Accurate pseudomorph identification may require more than appearance.

Epimorph

An epimorph forms as a coating or shell around another mineral. If the original mineral later dissolves or disappears, the shell may preserve a hollow impression of its shape. Usage can vary, and sellers should explain what relationship they mean.

Cast

A mineral cast is an impression or replica of a former object or mineral shape created when material fills a cavity or coats a form that is later removed. Casts can preserve crystal forms, fossils, plant material, or sedimentary textures.

Twinning

Twinning occurs when two or more crystals share a specific crystallographic relationship. Twin laws differ by mineral. A pair of crystals touching is not automatically a twin; the structural relationship matters.

Cleavage, fracture, and break

• Cleavage: a mineral’s tendency to split along structural planes
• Fracture: the way it breaks when cleavage does not control the surface
• Fresh break: recent physical damage
• Natural contact or incomplete growth: an original formation feature rather than later damage

Review Hardness vs. Toughness vs. Cleavage before assessing durability.

Locality

Locality is where a specimen was found. Good locality information may include country, state or province, district, mine, quarry, level, vein, or pocket. Precision should reflect the evidence. A highly specific undocumented locality is not stronger than an honest broader one.

Provenance and ex-collection

Provenance is the documented ownership, acquisition, and label history of a specimen. “Ex-collection” means formerly owned by a named person or institution, but the claim should be supported by an old label, catalog number, invoice, auction record, or other documentation.

Read How to Read a Mineral Label for label and catalog terminology.

Type specimen

In mineralogy, type material is associated with the formal description and definition of a mineral species. This is a technical scientific designation, not a synonym for “typical example” or “best quality.” Claims involving type specimens require authoritative documentation.

Repaired, restored, stabilized, and mounted

• Repaired: broken parts were reattached
• Restored or reconstructed: missing or damaged areas were rebuilt or filled
• Stabilized: fragile material was strengthened with a consolidant or support
• Mounted: the specimen was attached to a base or display support

These treatments can be acceptable when disclosed. See Repaired, Stabilized, and Mounted Mineral Specimens.

Aesthetic, collectible, rare, and museum grade

These words are partly subjective and frequently used in marketing.

• Aesthetic: visually pleasing composition, color, contrast, balance, or form
• Collectible: worth collecting to someone; too broad to prove quality
• Rare: uncommon in a defined context, which should be explained
• Museum grade: not a regulated universal grade and often promotional

Ask what measurable feature supports the description. Read What Makes a Mineral Specimen Collectible?.

Frequently asked questions

Are thumbnail sizes standardized?

No single standard controls every seller. Many use similar conventions, but always check exact measurements.

Is a float specimen always more valuable?

No. Value depends on species, locality, completeness, damage, aesthetics, rarity, and documentation.

Does “on matrix” mean the specimen is natural?

Not necessarily. Crystals can be repaired onto matrix, glued to a base, reconstructed, or paired with unrelated material. Disclosure matters.

Is a contact considered damage?

A natural contact is a growth feature, though it can affect aesthetics and value. A fresh chip or break occurred after formation.

What is the difference between druzy and a cluster?

Druzy is a coating of many small crystals. A cluster is a broader term for multiple crystals growing together and may include large individual crystals.

Can a trade name be used in a catalog?

Yes, but record the mineral species separately and identify the trade name as commercial terminology.

Which term matters most when buying?

Exact species, dimensions, condition, locality, treatment, repair, and provenance matter more than promotional adjectives.

Use terminology to ask better questions

Explore crystals and stones, then preserve measurements and terminology with a collection journal or suitable storage system. A glossary should make a listing easier to evaluate—not make ordinary material sound mysterious.