Hemimorphite Identification Guide

What Hemimorphite Looks Like

Hemimorphite is a hydrous zinc silicate (Zn₄Si₂O₇(OH)₂·H₂O) and a secondary ore of zinc found in the oxidized zones of zinc deposits. Its most popular form is a sky-blue to blue-green botryoidal (grape-like) crust with a smooth, glassy to porcelain surface, resembling turquoise or chrysocolla. It also occurs as colorless to white sheaf-like clusters of thin bladed/tabular crystals with a vitreous luster. Some specimens are brown or grey.

• Color: sky-blue, blue-green, white, colorless, brown
• Transparency: transparent (crystals) to translucent/opaque (botryoidal)
• Luster: vitreous on crystals; silky to dull on crusts
• Habit: botryoidal/reniform crusts; fan-like sheaves of bladed crystals

Step-by-Step Field-ID Checklist

1. Look at the form. Blue botryoidal crusts or radiating bladed crystal fans are characteristic.
2. Test hardness. Hemimorphite (4.5–5) scratches with a knife only with difficulty and does not scratch glass easily — it is harder than calcite but softer than quartz.
3. Heft it. It feels moderately heavy due to zinc content (SG ~3.4–3.5).
4. Check the setting. Oxidized zinc ore zones ("gossan") with smithsonite, galena, or sphalerite favor hemimorphite.
5. Inspect color and crystals. Glassy bladed crystals plus blue crusts together strongly suggest hemimorphite.

Key Diagnostic Tests

• Mohs hardness: 4.5–5 — harder than calcite, softer than feldspar/quartz.
• Streak: white.
• Cleavage: one perfect cleavage in crystals.
• Specific gravity: ~3.4–3.5 — heavy for a pale silicate.
• Acid: dissolves slowly in HCl but does not effervesce (unlike smithsonite, which fizzes).
• Pyroelectric/piezoelectric: the asymmetric (hemimorphic) crystals can develop charge with heat — a namesake property.

Common Look-Alikes and How to Tell Them Apart

• Smithsonite (ZnCO₃): very similar blue-green botryoidal crusts, but smithsonite is a carbonate that fizzes in acid and is slightly heavier; hemimorphite does not effervesce.
• Chrysocolla: softer, often lower density, copper-bearing, and lacks bladed crystals; hemimorphite is harder and zinc-based.
• Turquoise: harder feeling, waxier, and a phosphate; lacks hemimorphite's glassy bladed crystal form.
• Prehnite / hemimorphite crystal fans: prehnite is greener and forms different botryoidal aggregates; chemistry and acid behavior differ.
• Aurichalcite: lighter, fibrous tufts that fizz in acid (carbonate).

The decisive separator from smithsonite is the acid test (hemimorphite does not fizz), backed by hardness ~5 and the bladed crystal habit.

Where Hemimorphite Is Found

Hemimorphite occurs in the oxidized weathering zones of zinc ore bodies. Famous sources include the blue botryoidal material from Wenshan, China, Mapimi (Durango, Mexico), the classic European deposits of Belgium and Poland, and U.S. localities such as the Mississippi Valley districts and Arizona.

Quick Field Summary

A blue-green botryoidal crust or fan of glassy bladed crystals that is moderately heavy, has a hardness near 5, and does not fizz in acid is hemimorphite — distinguished from acid-reactive smithsonite, softer chrysocolla, and waxy turquoise.