What is a micromount?
A micromount is a specimen trimmed and mounted permanently in a small box to be viewed only under a microscope. It is a format choice, not a size grade.
A micromount is a specimen trimmed small and mounted permanently in a box of about 25 mm, intended to be looked at only under a microscope at roughly 10 to 40 times. It is a presentation format rather than a size grade: some species, such as clinoclase with crystals to 9 mm, are micromount species by nature.
In short
- A micromount is defined by how it is viewed, not by how big it is. The specimen is trimmed to fit, mounted permanently so it presents the right face, and put in a labelled box that is opened rather than handled. The microscope is part of the specimen's definition.
- It is not a thumbnail. A thumbnail is a size grade — a specimen that fits a box of about 2.5 cm and is looked at with the naked eye or a loupe. A micromount may be the same physical size and is a different kind of object, because it is not intended to be viewed unaided at all.
- Some species can only be micromounts. Clinoclase reaches 9 mm at its recorded maximum. Langite reaches 7 mm. For a species like that, the micromount is not the cheap option; it is the only format in which the crystals are actually visible.
- It is the format where rarity is affordable. Species that exist only as microscopic crystals are collected almost exclusively this way, and a micromount collection can cover ground a cabinet collection cannot at any size.
- The mounting is permanent and that is the point. Once fixed at the correct orientation, the specimen is never handled again, which removes the main cause of damage to small, fragile secondary species.
| Format | Size | Viewed with | Handled? | What decides the choice |
|---|---|---|---|---|
| Micromount | Box about 25 mm; specimen trimmed to fit | Microscope, roughly 10–40× | No — mounted permanently | The crystals are too small to see unaided |
| Thumbnail | Fits a box of about 2.5 cm | Naked eye or loupe | Yes, carefully | A complete small specimen worth seeing whole |
| Miniature | About 3–5 cm | Naked eye | Yes | Trade grade for a small display specimen |
| Small cabinet | About 5–8 cm | Naked eye | Yes | Trade grade |
| Cabinet | About 8–13 cm | Naked eye | Yes | Display presence |
| Museum | Above about 13 cm | Naked eye | Rarely | Exceptional pieces and institutional display |
Why the format follows the species, not the budget
The most common misunderstanding about micromounts is that they are what you collect when you cannot afford large specimens. Sometimes that is true. More often the format is chosen because the species itself has a size ceiling, and above that ceiling nothing exists to buy at any price.
Clinoclase is the clean example. The Handbook of Mineralogy records crystals typically needlelike, to 9 mm. Nine millimetres is the species maximum ever recorded, not a typical size — most Cornish clinoclase shows needles of one to three millimetres. So a “large clinoclase crystal” does not exist, and a large clinoclase specimen means a large plate of matrix carrying small rosettes. The crystals are genuinely better seen at twenty times magnification than in the hand, and that is a statement about the mineral rather than about the collector.
Langite is the same: crystals to 7 mm, commonly skeletal, with the repeated twinning that produces the snowflake groupings the species is collected for. You cannot see a snowflake grouping without magnification.
The rule, and it is the one that reframes the whole format: the format follows the species, not the budget. A micromounted clinoclase is not a lesser object than a cabinet fluorite. It is the correct presentation of a mineral that never grows large, and a badly chosen cabinet-sized piece of the same species is the worse specimen, because most of what you are storing is country rock.
Micromount or thumbnail: the distinction people get wrong
These two are routinely used as if they meant the same thing, and they describe different properties.
Thumbnail is a size grade. It sits at the bottom of the same scale as miniature, small cabinet and cabinet, and it means a specimen that fits a box of roughly 2.5 cm. A thumbnail is meant to be looked at with the naked eye, and a good one is a complete, well-proportioned, aesthetically composed specimen in miniature. The grades are covered on specimen sizes and grading.
Micromount is a presentation format. It says the specimen has been trimmed and fixed in a box for microscope viewing. A micromount may well be physically smaller than a thumbnail, or about the same, and the distinction is not about the millimetres.
The practical test is whether the specimen rewards being looked at unaided. If the interest of the piece is visible in the hand, it is a thumbnail, however small. If the interest of the piece only appears under magnification, it is a micromount, and putting it in a thumbnail box on a shelf wastes it.
There is a middle grade, the toenail — trade slang for a specimen between thumbnail and miniature, roughly 2.5 to 3 cm. It is a size word like the others and carries no implication about viewing.
How a micromount is actually made
The process is simple, and all of it is reversible except the trimming.
Trim the specimen down to the interesting area. This is the part that requires nerve and the part that cannot be undone. Remove matrix that carries nothing, working with nippers or a small trim saw, always away from the crystals, and stop earlier than you think you should. A micromount with a little spare matrix is fine; one with a crystal clipped off is not.
Mount it so the best face presents at the right angle to the viewer. The traditional method is a small plastic or cork pedestal fixed inside the box, with the specimen attached to the pedestal by a removable adhesive — a water-soluble glue or a wax, not an epoxy. Reversibility matters: a specimen may need to be remounted, re-examined or analysed, and an irreversible mounting removes that option permanently.
Box it and label it. The standard micromount box is a small hinged plastic box of about 25 mm with a clear lid. The label goes on the box and carries the species, the locality, the collection number and — importantly for micromounts — the determination basis, because micro material is disproportionately likely to be a species that cannot be identified by eye. Our cataloguing conventions cover the three-state convention this needs.
Never wash a mounted micro. The species that end up as micromounts — secondary arsenates, sulphates, delicate acicular growths — are exactly the ones that cleaning destroys. See how to clean mineral specimens.
What you need to look at them, and what you do not
A stereo microscope, not a compound one. This is the one piece of equipment that matters and the one most commonly bought wrong. A compound microscope — the school biology kind, with a slide stage — gives high magnification, a flat image and no working distance, and is useless for minerals. A stereo or dissecting microscope gives two eyepieces, a three-dimensional image, a long working distance and a wide field, which is exactly what a crystal group needs.
Magnification of about 10 to 40 times covers nearly everything. Higher magnification sounds better and is usually worse: the depth of field collapses, so only a sliver of the specimen is in focus at once, and the field of view becomes too small to see a grouping. Most micromounters spend most of their time between 15 and 30 times.
Lighting matters more than optics. A ring light gives even illumination and flattens the specimen; a single adjustable point source raked across the crystals shows the faces, the lustre and the terminations. Serious micromounters use both and switch between them.
What you do not need: an expensive microscope to start. A modest stereo instrument with good lighting shows more than a fine one with poor lighting. And you do not need a UV lamp — that is a separate question with a separate answer, and mostly no.
Micro material is where a great deal of the interest in British mineralogy now sits, because the classic localities are worked out for large specimens and are not worked out for small ones. Species we are looking for, in any format, are on the wanted list, and the rest of our collecting guides cover the buying and condition questions that apply at every size.