Mineral Species Categorization Guide
🔹 Rarity
What it means: How physically scarce a species is, based on both geological distribution (number of known localities) and market availability. This is a supply-side measure of availability to collectors.
Widely distributed and readily available. Found in numerous localities worldwide (often hundreds or thousands), and specimens are easily obtainable from dealers or at shows. Common minerals tend to be inexpensive and occur in bulk.
Quartz (found in over 27,000 localities), Calcite, Pyrite, Fluorite – all are found globally and sold in abundance.
Even fine crystals of these species are generally accessible, so they merit a "Common" rating. If a species is found on every continent and routinely appears in dealer stock, it belongs here.
Moderately distributed or less routinely seen. Found in a fair number of localities (perhaps a few dozen to a few hundred) but not as ubiquitous as common minerals. Good specimens may only come from a handful of regions, making them less abundant on the market.
Wulfenite (lead molybdate found in many mines but fine crystals mainly from select locales in Arizona, Mexico, etc.).
Dioptase (brilliant green copper silicate from a few classic localities in Namibia, Congo, etc.).
Celestine (Celestite) (occurs in several areas but fine blue crystals mainly from Madagascar or Ohio).
These minerals are obtainable and not "rare" per se, but you won't see them in every dealer's tray. An Uncommon rating fits species with limited noteworthy sources or intermittent supply.
Limited distribution or scarce supply in collections. Known from relatively few localities worldwide (perhaps on the order of 5–20 significant sources) or from one major deposit that produced only a limited number of specimens. Minerals in this class are infrequently encountered for sale and often command premium prices when good examples appear.
Phosphophyllite – found notably at one Bolivian mine and a few minor localities; fine crystals are coveted because the species is geologically scarce.
Benitoite – essentially from one deposit in California (plus a couple of tiny finds elsewhere).
Cavansite – historically only abundant at one Indian locality (Wagholi Quarry), now mined out.
Assign "Rare" to species with a very constrained natural occurrence or ones that seldom reach the market in any quantity. Note: In mineralogy literature, "rare" is sometimes defined strictly as occurring at 5 or fewer localities, but in this guide we reserve Rare for minerals that, while not ultra-rare scientifically, are hard to find for collectors.
Exceptionally scarce minerals with very few known occurrences or specimens. These fit the strictest rarity definition – perhaps only one, two, or a handful of localities are known worldwide. In many cases, only a small number of specimens exist (sometimes a single known specimen). Market availability is virtually zero; specimens typically appear as micromounts or in museum collections.
Fingerite (only found at Izalco volcano in El Salvador; fewer than a dozen specimens exist).
Kyawthuite (one known crystal, from Myanmar).
Edoylerite (rare mercury mineral from one locality).
Painite was once in this category with only 3 crystals known until 2001.
Use "Extremely Rare" sparingly – it denotes the rarest of the rare, species with <5 find spots or only trace specimens in existence. These often correspond to the "rare minerals" of mineralogical studies (over half of all ~5,000 known species fall into ≤5 localities, though most are microscopic).
Other Notes on Rarity
If a mineral is known from only one locality but that locality produced plentiful material, consider downgrading the rarity rating. For example, charoite is only found in one deposit in Russia, yet one can "buy a dozen pieces at any major show"; thus charoite, despite one locality, would rank Uncommon rather than Rare because of its ample supply.
Conversely, a mineral found in, say, 10 localities but only ever in tiny micro crystals and never offered for sale might warrant a Rare rating. Always weigh both the geologic rarity and how many specimens are actually out there in collections.
For borderline cases, consider both how many localities produce the mineral and how often good specimens are available for collectors.
💎 Collector Interest Rating
What it means: This dimension gauges the level of enthusiasm and demand a species generates among collectors. It considers factors like aesthetic appeal, historical prestige, "buzz" in the community, and typical pricing at shows or auctions. The scale ranges from Very High Interest (glamour species that almost every collector covets) down to Low Interest (species only a few specialists pursue).
Iconic, "must-have" species with broad collector appeal and top-tier desirability. These minerals are highly sought after across the hobby. They tend to be visually stunning or historically significant, and fine specimens often headline auctions or museum exhibits. Collectors will pay premium prices for top examples, and even typical specimens are in strong demand.
Native Gold — almost universally coveted; crystallized specimens fetch six-figure sums.
Emerald (Beryl) — gem-quality emerald crystals from Colombia or Zambia are prized for deep green color.
Tourmaline (Elbaite) — especially multi-colored gem tourmalines from Brazil or Afghanistan.
Rhodochrosite — cherry-red rhombohedral crystals from Sweet Home Mine (Colorado).
Very High Interest species command high prices even for small specimens, generate "buzz" at major shows, and are frequently mentioned as favorites in collector forums. Auction results confirm this level of interest; for example, a world-class Linarite sold for $158,500, setting a record and creating palpable buzz.
Popular and desirable species, though not quite at the apex of demand. Many collectors actively seek these minerals, and fine examples can be quite valuable, but they might be a step below the "must-haves" or perhaps more available. Species in this category are often colorful or aesthetic, frequently seen in competitive displays, and well-represented in advanced collections.
Fluorite — common mineral with extraordinary color range; collectors worldwide love fluorite.
Azurite — deep blue, lustrous crystals from Tsumeb, Namibia or Milpillas, Mexico.
Aquamarine (Beryl) — sky-blue gem beryl crystals from Brazil, Pakistan, etc.
Distinguish Very High vs. High by asking: is this species almost universally desired, or just broadly popular? High Interest species are well-liked but perhaps not everyone's holy grail. They also might be more common (thus a bit less exclusive) than the Very High group. Pricing helps gauge this — top fluorites or aquamarines can cost tens of thousands, but generally less than a top tourmaline or gold specimen of similar caliber.
Species that attract interest mainly from certain segments or when specimens are exceptional. These minerals are of interest to many collectors but not to the extent of the above categories. Often they are either very common species that only garner excitement when unusually fine, or rarer species that are appreciated mostly by specialists. The average collector might have a few of these, but they are not universally pursued.
Calcite — ubiquitous mineral that normally is low-value, yet incredibly varied and can be breathtaking.
Galena — lead sulfide with bright metallic cubes; common in many ore veins.
A very common mineral like quartz would usually be Moderate interest — except extraordinary examples can elevate interest transiently. For instance, a spectacular quartz specimen like "La Madona Rosa" (the famous large rose quartz) set an auction record of $662,500, showing that exceptional specimens of even moderate-interest species can generate high interest. But overall, quartz as a species remains moderate interest.
Niche or low-demand species — few collectors actively seek these, except perhaps specialists. Minerals in this category either lack aesthetic appeal, are extremely common and dull, or are so rare and microscopic that only completionist collectors bother with them. They typically carry low market value (unless for scientific value) and generate little "buzz."
Common rock-formers: e.g. Ilmenite, Olivine (Peridotite) in matrix — important in geology but usually black or greenish masses that collectors find unexciting.
Clays like kaolinite or massive ores like bauxite.
Unspectacular rare species that form only tiny grains or crusts.
Use Low Interest for species that the average collector would not include unless focusing on that specific niche. Even if a Low-Interest mineral is geologically common, collectors might ignore it (e.g., Albite Feldspar is everywhere, but few display a plain albite). Conversely, if a mineral is exceedingly rare but just a black speck on rock (no beauty or fame), it also slots here in terms of collector interest.
Influencing Factors
Aesthetic appeal is king for high interest (bright colors, good crystal form, transparency all boost a mineral's appeal). Historical or type-locality significance can elevate interest.
Pricing and "buzz" follow interest: minerals in Very High or High interest categories often correspond to high market prices and fierce competition to acquire. Indeed, public auctions have demonstrated that fine and rare minerals are an emerging collectible class with serious bidding wars.
When in doubt, consider whether the mineral would be on a "Top 50 minerals" list for a general collector. For example, Pyrite is common and cheap, but its brilliant metallic cubes are iconic — most collectors have one good pyrite, so interest might be moderate (it's well-known but not particularly coveted beyond a representative piece).
🛡️ Display/Storage Stability
What it means: This dimension rates how stable a mineral species is under typical collection and display conditions. Not all minerals are as enduring as quartz — some can alter, fade, or deteriorate if exposed to light, air, humidity, or heat. The Stability rating helps collectors anticipate care requirements.
Hardy and unreactive under normal conditions. These minerals do not noticeably change, corrode, or lose quality over time in a typical display. They can handle normal light levels and household humidity without issue. The vast majority of common collectible minerals fall in this category.
Quartz (silicon dioxide) — chemically inert, doesn't alter or fade.
Garnet, Tourmaline, Beryl (emerald, aquamarine), Spinel, Topaz — most silicates and oxides are quite stable.
Calcite and Fluorite — generally stable (they might cleave if knocked, but they won't decompose on their own; just avoid acids).
Gold, Native Copper, Silver — metals are stable, though silver can tarnish (a thin film of silver sulfide) under humidity and sulfur.
A Stable rating means no special care is required beyond standard dusting and sensible storage. Some "stable" minerals can have minor issues (e.g. amethyst quartz can fade to pale if left in direct sun for years), but under typical indoor lighting they're fine. Always double-check if a species has any known sensitivities: if none are commonly reported, mark it Stable.
Generally holds up, but needs some care to prevent deterioration. Minerals in this category can be displayed, but collectors should take precautions with lighting, humidity, or handling to maintain them long-term. They might slowly alter under adverse conditions or have minor sensitivities.
Pyrite (FeS₂) — infamous for "pyrite disease," a condition where pyrite oxidizes in humid air to produce sulfuric acid and iron sulfate, leading to a crumbly white powder on the specimen. In a dry cabinet (< ~50% humidity) pyrite can remain unchanged for decades.
Cuprite — can develop a dull oxide coating over time; keep out of damp conditions.
Halite (salt) — water-soluble; fine in low humidity but can slowly "sweat" or dissolve in humid conditions.
Fluorite — mostly stable, but some deep purple fluorites may fade under prolonged sunlight or UV exposure.
Uranium minerals like Autunite, Torbernite — these contain water in their crystal structure and will gradually lose water, causing color dulling over years.
Opal — contains water and can "craze" (develop cracks) if it dries out or is subjected to temperature swings.
Assign Moderately Stable to species that can be showcased but need a controlled environment or gentle handling to avoid slow alteration. Provide a note about the specific risk (e.g. "keep pyrite dry" or "avoid direct sun on fluorite"). Many sulfates, hydrates, and moderate Mohs hardness minerals fall here.
Delicate species that are prone to damage or alteration even in normal conditions; special measures required. These minerals can deteriorate rapidly if simply left on a shelf. Collectors must usually store them in dark, sealed containers or inert atmospheres to preserve them. Often, unstable minerals are those that react to light (photo-sensitive), air (oxidize), or moisture (hydrate/dehydrate easily).
Realgar (AsS) — a prime example of an unstable mineral. Realgar's beautiful red crystals will gradually turn into a different mineral (pararealgar) and then a powdery yellow film when exposed to light. Within months of exposure to bright light, realgar crumbles into yellow dust.
Vivianite (Fe³⁺(PO₄)₂·8H₂O) — fresh vivianite is colorless to pale blue, but it oxidizes on exposure to air/light, turning deep blue, then dark green, and eventually nearly black. This color change is permanent and can occur within hours to days in sunlight.
Cryolite (Na₃AlF₆) — a rare halide that is slightly soluble in water. Exposure to humidity or handling with moist fingers can etch or dull it.
Proustite and Pyrargyrite (Ag₃AsS₃ / Ag₃SbS₃) — the ruby-red silver ores known to "dim" under light. Bright light will darken their crystals and form a black film of silver sulfosalts.
Hydrated Salts (e.g., Melanterite, Mirabilite) — will dehydrate and crumble to powder in normal room conditions; these are so unstable they're usually only preserved in sealed containers.
Use the Unstable label for any species known to require extraordinary care. Often the label will coincide with applying the "Light-Sensitive" or similar tag. If you mark a species Unstable, include a note about the specific sensitivity (light, air, moisture) so collectors know why it's unstable. Unstable minerals may still be collected (some collectors love the challenge), but they must be handled almost like perishable goods.
General Notes on Stability
This category is about a mineral's chemical or physical stability over time on display. It is not about fragility per se (e.g., crystals that break easily due to softness are not "unstable" in this context; that could be noted separately as "fragile"). So, a brittle mineral that doesn't alter (like cerussite, which is soft and prone to breakage but doesn't self-alter) is actually stable (just handle carefully). Conversely, a mineral could be quite hard but still unstable chemically (e.g., some sulfides).
When classifying, ask: "Will this species change or degrade if I leave it alone on a shelf for years?" If yes, it's unstable; if maybe under some conditions, moderately; if no, stable.
When in doubt, research known issues: for example, a quick check on Mindat or literature may reveal "this mineral alters to X when exposed to air" — a clear sign of instability. Use authoritative sources or known museum conservation practices as a guide. Museums maintain lists of minerals that should be kept in climate-controlled or dark storage, which aligns with our Unstable list.
Edge Cases
Azurite is generally stable, but in some cases azurite can alter to malachite if in contact with water over geologic time; however, in a display setting, azurite is safe (so we call it Stable). Malachite can have surface dehydration if very fresh, but is effectively stable.
Egyptian salt natron effloresces in air — unstable.
If a species has multiple forms, consider the typical collector specimen: e.g., vivianite — any exposed crystal will darken, so unstable, even though chemically you could keep it anoxic to slow it (beyond normal practice).
For borderline minerals like Erythrite (cobalt bloom, can fade from bright pink to pale under light), you might lean Unstable if evidence shows noticeable fading within a few years. When assigning stability, it's better to caution on the side of instability if a species has any well-known deterioration modes; this alerts the collector to take preventive steps.
🏷️ Optional Tags for Special Properties
Beyond the main ratings above, this guide provides optional tags -- keywords that collectors can attach to a mineral species entry to denote special characteristics or considerations. These tags help flag minerals with noteworthy traits (good or bad) that might cut across rarity/interest/stability. Tags are supplemental and can be used in combination. For example, a species could be rated Rare, High Interest, Moderately Stable, and then tagged "Fluorescent" and "Radioactive" if both apply.
Below is a curated set of recommended tags, each with a definition, usage guideline, and example species. Assign tags where relevant, but avoid over-tagging; use them for prominent features that a collector would want to know at a glance. For instance, apply "Fluorescent" only if the fluorescence is strong or notable (many minerals have minor fluorescence under UV, but we reserve the tag for those famous for it). These tags capture properties often discussed in collector circles and literature (including Mindat and dealer catalogs).
Glows under ultraviolet (UV) light. Tag minerals that exhibit notable fluorescence, meaning they emit bright visible light under UV (shortwave and/or longwave). This tag is typically applied to species known and celebrated for fluorescence -- either widely (as a species property) or from specific locales.
Willemite & Calcite -- the quintessential fluorescent duo from Franklin, New Jersey. Willemite fluoresces bright green and calcite red under shortwave UV.
Scheelite -- fluoresces intense blue-white under shortwave UV (used by geologists to find scheelite ore).
Fluorite -- many fluorites fluoresce (blue or purple typically), though not all; certain localities like Rogerley Mine (UK) are known for daylight fluorescence.
Hackmanite (Sodalite) -- shows Tenebrescence and fluorescence (orange under UV) especially from Afghanistan or Ontario.
Autunite -- fluorescent neon yellow-green under UV.
Use "Fluorescent" for minerals that reliably fluoresce in most specimens or for classic fluorescent localities. If only certain localities or activators cause fluorescence, you might still tag the species but consider adding a note (e.g. "fluorescent, especially from Franklin, NJ due to Mn activation").
Do not tag if fluorescence is very weak or rare. When you tag Fluorescent, you alert collectors that they may want to test the specimen under UV or display it with UV lighting.
If a species' fluorescence is due to common activators and it's a well-known trait, tagging is warranted. But if only a few specimens fluoresce, you can skip tagging for the species globally.
Contains radioactive elements (U, Th, K) at levels requiring caution. Tag minerals as "Radioactive" if they contain significant uranium, thorium, or other radioactive constituents that emit ionizing radiation. This typically includes uranium ores, thorium minerals, and some potassium-rich minerals.
Uraninite (Pitchblende) - primary uranium ore mineral, highly radioactive specimens that can fog photographic film.
Autunite and Torbernite - green and blue-green hydrated uranium phosphates that are moderately radioactive and commonly fluorescent.
Thorite - thorium silicate mineral that is significantly radioactive.
Carnotite - bright yellow uranium mineral that was historically mined for radium.
Euxenite and Monazite - rare earth minerals that commonly contain thorium or uranium.
This tag is a safety flag. Use it for species that will set off a Geiger counter appreciably or that require handling/storage considerations for radioactivity.
Tagging something Radioactive suggests one should avoid prolonged close exposure or inhalation/ingestion of dust, store away from sensitive electronics or documents, and perhaps use a display case that vents any radon.
Do not tag minerals that only have trivial radioactivity. Typically, if a species has > a few % of U or Th in formula, it's a candidate. You may combine "Radioactive" with "Fluorescent" (e.g., autunite is both).
Prone to damage or alteration upon exposure to light. This tag highlights minerals that should be kept in the dark to preserve them. Often these are also rated Unstable in the Stability category. Use "Light-Sensitive" when a mineral's color or structure changes under light (usually ultraviolet component of light is the culprit, but even visible light can do it for some).
Realgar -- will irreversibly turn to powder in light; absolutely light-sensitive.
Proustite -- "Ruby silver" that darkens and loses transparency with exposure, developing a dark film of silver -- a classic light-sensitive specimen.
Vivianite -- oxidizes and blackens with light/air (store in dark).
Amethyst -- can fade with prolonged sunlight (UV) exposure; not as urgent as realgar, but high-end amethyst geodes are often kept out of direct sun.
Kunzite (Spodumene) -- the delicate pink color can fade to near-colorless if left in strong sunlight.
Erythrite (Cobalt bloom) -- bright purple-red when fresh, but can dull on exposure to light/air over time.
If a species is tagged Light-Sensitive, collectors should display it under controlled lighting (or not at all) and use UV-protective glass if possible.
This tag often overlaps with Unstable, but not always -- e.g., some minerals might only lose color (fading) but not crumble. The tag is also a heads-up for photography: light-sensitive minerals should not be left under strong studio lights for too long.
Only use this tag for well-documented cases. Reserve "Light-Sensitive" for those that within a human timeframe (months to years) will show changes. If light is the main trigger for deterioration, use this tag.
Typically found only as microscopic or very small crystals. Use this tag for mineral species that do not form appreciable macroscopic crystals or attractive specimens visible to the naked eye. These are species usually obtained and observed as micromounts (using a hand lens or microscope).
Minerals of the Franklin Furnace or Tsumeb type that are known only as micro inclusions or crusts.
Ludlockite -- at Tsumeb it forms tiny orange fibers; aesthetic under magnification but seldom seen as large pieces.
Tellurium minerals like Calaverite, Sylvanite often need a loupe to see crystal forms.
Rare earth oxides, sulfosalts (many only found as micro grains).
Chlorargyrite (AgCl) can form visible crystals, but commonly it's little waxy blobs -- might be tagged micro only if typical specimens are BB-sized.
Tag "Micro Only" for species where collectors essentially must use a microscope to appreciate them. This helps differentiate "display species" from "reference species" in a collection.
If a species occasionally forms a large crystal but 95% of the time doesn't, you might still tag it (with a note like "usually micro; exception: one find produced 1cm crystals").
But if a species regularly has both micro and macro examples, don't tag it. The purpose of this tag is to set expectation -- a collector cataloging species knows that if it's tagged Micro Only, they likely will acquire it as a micromount.
A species with special historic significance or "classic" collector status. This tag is for minerals that carry an aura of history or are strongly associated with classic localities and old collections. It may be a species that was important in the early days of mineralogy, or one that comes from famed mines often mentioned in literature. The tag can apply to species that might not be rare but have enduring historic interest.
Azurite -- used as a pigment since antiquity and collected for centuries; a classic copper mineral from localities like Chessy (France) and Tsumeb (Namibia).
Haüyne -- named after Abbé Haüy (father of crystallography), discovered in 1807; historic as one of the first described feldspathoid gems.
Crocoite -- classic lead chromate; known from Siberia since the 18th century, it led to the discovery of the element chromium.
Hematite -- the ancient "iron ore" and red pigment (red ochre) used by humans for millennia; as a species, not rare, but historic.
Galena -- principal lead ore since Roman times, yielding silver (at localities like Laurium, Greece); again common but historic.
Use Classic/Historic to flag species that a seasoned collector or historian would recognize as having a special legacy. This is somewhat subjective, but clues include: first described long ago (1700s-1800s), significant role in mining history or scientific developments, or synonymous with a particular classic mine.
A "Classic" tag doesn't necessarily correlate with high value -- it's more about cultural or historical cachet. Often, classic minerals come from localities that are long closed, making old specimens treasured.
Use sparingly and with context; you might combine it with another tag if relevant. The benefit of tagging Classic/Historic is to highlight minerals that one might encounter in literature or museum legacy collections.
Mineral species that produce gemstones or facet-grade material. Tag a species "Gem Mineral" if it is well-known for yielding transparent, facettable crystals or is commonly used in jewelry. Essentially, these are minerals that have alter egos as precious or semi-precious stones.
Corundum -- includes Ruby and Sapphire, obvious gem minerals; even if a collector's specimen is a rough crystal, the species is a gem category.
Beryl -- includes Emerald, Aquamarine, Morganite; beryl is quintessential gem mineral.
Tourmaline -- (Elbaite, etc.) many tourmalines are cut as gems; the species is prized for both specimens and gemstones.
Topaz, Spinel, Garnet, Zircon, Spodumene (Kunzite, Hiddenite), Quartz varieties (Amethyst, Citrine) -- all these are gem minerals.
Turquoise, Opal (non-crystalline gem materials, but turquoise is a phosphate mineral, opal a mineraloid -- one can still tag Opal as gem material).
The Gem Mineral tag is useful to signal that a species has a foot in both the mineral collecting hobby and the gem trade. Such minerals often have added interest because of their value and recognizability.
Do not tag something just because it's pretty -- the key is usage as a gemstone. If a species is frequently listed in gemological lists, it qualifies for this tag.
Tagging gem minerals helps in sorting your collection database if one wants to filter all "gem species." It can also hint at why certain species have High interest (gem minerals often do because of crossover collectors and higher prices).