Mottramite Collectors Guide

Ojuela is famous for velvety botryoidal and stalactitic mottramite, typically deep green to nearly black-green, carpeting iron-rich gossan. Classic combinations pair mossy mottramite with butterscotch to orange wulfenite, or with calcite and limonite for strong texture and color contrast. Though true euhedral crystals are rare here, the best Ojuela coatings are intensely chatoyant and sculptural, forming aesthetic “landscapes” across matrix. Because Ojuela has produced a steady stream of material over the years, it offers excellent value—especially for richly colored, unabraded coatings on solid matrix.

Collector’s Guide

Evaluating Specimen Quality

• Color and Saturation:

  • Most desirable are vivid, saturated greens: grass, pine, or mossy tones that read clearly in normal lighting. Very dark, nearly black coatings can hide detail; bright, lively greens command premiums.
  • Subtle yellow-green highlights or zoning can add interest. Uniform, rich color across the display face is preferred.

• Luster and Surface Texture:

  • Two winning looks: silky-velvety botryoidal coatings with chatoyancy, and sparkling microcrystalline druses that glitter under light.
  • Dull, matte surfaces are less desirable unless compensated by outstanding associations or sculptural form.

• Crystal Form and Habit:

  • True, sharp crystals are rare and most strongly associated with Tsumeb; even small, undamaged clusters are valuable.
  • Botryoidal, stalactitic, and reniform growths are classic; look for crisp, well-formed hemispheres with clean, undamaged skin.
  • Stalactitic “fingers” or sculptural carpets that flow around matrix contours can be very aesthetic.
  • Pseudomorphs or partial replacements on wulfenite edges, or mottramite delicately dusting reticulated cerussite, are highly collectible.

• Associations and Matrix:

  • Top combinations include: mottramite with wulfenite (Ojuela, San Pedro Corralitos), reticulated cerussite (Touissit, Tsumeb), calcite or dolomite (Tsumeb), and iron-oxide gossan providing rugged contrast.
  • Balanced composition matters: avoid crowded, messy matrices where mottramite is hidden; aim for open display fields with strong color contrast.

• Condition and Stability:

  • Mottramite is brittle and can shed microcrystals; examine for rubbing or “bald” patches on the velvety surface.
  • Check edges of botryoids for frosting or abrasion; pristine skins are sharply defined and even.
  • Heavy matrix plus delicate coatings means chips occur easily—prioritize minimal, non-distracting damage on the prime face.

• Size and Aesthetics:

  • Quality trumps size: a smaller, intensely colored, undamaged piece will outshine a large, dark or abraded one.
  • Under LED case lighting, the best mottramite comes alive—look for responsiveness to light (sparkle or shimmer).

Detecting Repairs or Treatments

• Stabilization:

  • Because surfaces can be crumbly, some pieces are consolidated with clear resins (e.g., Paraloid). Look for localized glossy patches or a slightly “plastic” sheen in crevices. Disclosure is best practice and generally acceptable for fragile coatings.

• Recoloring or Coatings:

  • Beware of artificially enhanced color via dyed consolidants or paint. Suspect areas may show uniform, unnatural hue pooling in pits. A cotton swab with acetone (used cautiously, away from display surface) can reveal dye on non-critical back areas.

• Composite Assemblies:

  • Verify that mottramite–wulfenite combinations are natural to the locality and matrix—mismatched matrices, odd glue halos, or different patinas can indicate assembled specimens.

Care and Storage

• Handling:

  • Treat as delicate. Support the matrix with two hands; avoid brushing or touching velvety surfaces which can shed. Heavy SG means a small nudge can cause significant impact damage.

• Cleaning:

  • Dust gently with a soft air bulb or very soft sable brush; avoid vigorous brushing of botryoidal skins.
  • Rinse briefly with lukewarm distilled water only if necessary; pat dry. Do not use ultrasonic cleaners or steam—vibration and heat can cause shedding or cracks.
  • Avoid acids and aggressive cleaners (including strong chelators and oxidizers). Even mild chemical baths (e.g., dithionite “Iron Out”) may alter color or attack delicate associations—test only on inconspicuous areas and preferably avoid.

• Light, Heat, and Environment:

  • Colors are generally stable under normal display lighting. Use moderate LED lighting and avoid prolonged high heat or intense direct sun that can stress glues or matrix.
  • Keep in a stable, dry environment; avoid high humidity that may encourage matrix deterioration.

• Storage:

  • Provide padded supports that do not contact the mottramite surface. Use microcellular foam or custom stands to secure heavy pieces.
  • Separate specimens to prevent abrasion. In seismic or high-vibration areas, tack bases carefully (avoiding contact with coated surfaces).

• Health Note:

  • Mottramite contains lead—wash hands after handling and keep dust away from living areas.