THE WAND & THE CRYSTAL BALL SOCIETY · PECKHAM

Epidote: The Green That Reads Black

What it is and how the crystals form

Epidote is a calcium‑iron aluminium sorosilicate that typically appears in shades of green, ranging from pale pistachio to deep olive. It belongs to the epidote group, which also includes clino‑ and andradite varieties. The mineral crystallises in the monoclinic system, producing prismatic to tabular crystals that often display a characteristic striated habit. Epidote forms during low‑ to medium‑grade metamorphism of calcium‑rich rocks such as limestones, marbles and schists, and it is also a common product of hydrothermal alteration in greenschist‑facies terranes. In the field you will find it filling veins, replacing feldspar, or occurring as disseminated grains within metamorphic matrices.

How to judge a good specimen

A high‑quality epidote piece should meet several visual and physical criteria:

• Colour consistency: Uniform, vivid green without excessive brown or yellow zoning.
• Crystal form: Well‑developed prisms or tabular crystals with clear striations and sharp terminations.
• Transparency: Translucent to semi‑transparent material is preferable; opaque masses are less desirable unless they display exceptional crystal size.
• Surface finish: A smooth, unweathered surface that shows the natural luster of epidote, typically a vitreous to resinous sheen.
• Inclusion content: Minimal secondary inclusions; occasional quartz or calcite inclusions are acceptable if they do not obscure the crystal habit.
• Size and weight: Larger, well‑formed crystals command higher interest, but a collection of smaller, perfectly formed crystals can also be valuable when displayed together.

What affects the price

The market value of epidote is driven by a combination of rarity, quality and provenance. The following factors are most influential:

• Locality: Specimens from classic metamorphic districts such as the Scottish Highlands, the Alps or the Harz Mountains tend to fetch higher prices due to their recognised geological significance.
• Crystal size and habit: Large, well‑formed prisms with minimal damage are priced above smaller, irregular fragments.
• Colour intensity: Deep, saturated greens are more sought after than pale or mottled specimens.
• Cut and polish: Professionally cut and polished pieces, especially those prepared for display, command a premium over rough material.
• Documentation: A clear provenance record, including a reputable dealer’s certificate, adds confidence and can increase the asking price.
• Market demand: Seasonal interest from collectors, museums or educational institutions can cause short‑term price fluctuations.

How to tell it from lookalikes

Epidote is often confused with minerals such as chlorite, actinolite, and green feldspar. Use these distinguishing features to avoid misidentification:

• Hardness: Epidote rates 6–7 on the Mohs scale, noticeably harder than chlorite (2–3) and comparable to actinolite (5–6). A simple scratch test with a steel nail can be informative.
• Cleavage: Epidote exhibits two directions of perfect cleavage at about 85° and 95°, whereas actinolite shows a single perfect cleavage at 56°.
• Refractive index: If a refractometer is available, epidote’s index (1.73–1.75) is higher than that of most chlorites (≈1.60).
• Crystal habit: The striated, prismatic habit of epidote is distinctive; chlorite typically forms platy, micaceous flakes, and green feldspar displays blocky, tabular crystals without striations.
• Acid test: A dilute hydrochloric acid drop will effervesce on calcite but not on epidote, helping to rule out carbonate contaminants.

Care and safety

Epidote is chemically stable under normal indoor conditions, but proper handling ensures longevity and safety:

• Cleaning: Use a soft, lint‑free cloth and mild soap solution. Avoid abrasive pads or harsh chemicals that could dull the surface.
• Storage: Keep specimens in a dry, temperature‑controlled environment. Excess humidity can promote surface mould on porous host rocks.
• Handling: Wear gloves when moving large pieces to prevent oils from your skin transferring to the mineral surface.
• Safety: While epidote itself is non‑toxic, some associated minerals (e.g., arsenopyrite) may be present in the matrix. If you suspect contamination, wear a dust mask and wash hands thoroughly after handling.

Choosing a photographed, priced piece over a mystery box is simple: a clear image and documented price give you confidence in the specimen’s quality, provenance and value before you commit. With that transparency, you avoid the disappointment of unexpected flaws and ensure that your purchase truly enhances your collection.

Peckham Crystals · The Wand & The Crystal Ball Society, Rye Lane Market, Peckham, London SE15 5BY ·
info@increatus.com · 07961 945999. Prices are UK retail estimates, not guarantees.