Barium Feldspar Identification Guide
How to recognize barium-rich feldspars such as celsian and hyalophane by their feldspar habit, cleavage, and the field clues that separate them from common feldspars.
Read the full Barium Feldspar encyclopedia entry →
What Barium Feldspar Looks Like
"Barium feldspar" refers to the celsian (BaAl2Si2O8)–hyalophane series, feldspars in which barium substitutes for potassium. They look like ordinary feldspar but tend to be denser. Typical traits:
- Color: colorless, white, gray, pale yellow, or faintly pink.
- Luster: vitreous to slightly pearly on cleavage faces.
- Transparency: transparent to translucent.
- Habit: stubby prismatic or tabular crystals and massive grains; like other feldspars, it shows two good cleavages meeting near 90°.
Field-ID Checklist
- Confirm a feldspar look: blocky crystals or grains with flat, reflective cleavage planes.
- Find two cleavage directions intersecting at roughly 90° (monoclinic, near-right-angle).
- Note that the specimen feels heavier than expected for a pale feldspar.
- Check the geologic setting: barium feldspars favor manganese deposits and metamorphic rocks.
- Because field separation from common feldspar is hard, record the host assemblage (e.g., associated Mn or Ba minerals).
Key Diagnostic Tests
- Mohs hardness: 6–6.5, like other feldspars; it scratches glass and is not scratched by a steel knife.
- Streak: white.
- Cleavage: two good cleavages at about 90°, plus a poorer third direction.
- Density: elevated for a feldspar — celsian reaches ~3.1–3.4 g/cm³ versus ~2.55–2.76 for ordinary feldspar. This heft is the single best field clue.
- No acid reaction; not magnetic.
- Fluorescence: some hyalophane/celsian fluoresce, but this is not diagnostic alone.
Common Look-Alikes and How to Tell Them Apart
- Orthoclase / microcline (K-feldspar): nearly identical appearance and hardness, but distinctly lighter (density ~2.56). A heft comparison or specific-gravity measurement separates them.
- Albite / plagioclase: plagioclase often shows fine striations (albite twinning) on cleavage faces; barium feldspars usually lack these and are denser.
- Quartz: harder (7), no cleavage, conchoidal fracture — quartz lacks the flat cleavage planes of feldspar.
- Barite: a barium sulfate, also heavy, but much softer (3–3.5) and reacts differently; barite has three cleavages and lower hardness.
- Scapolite: can resemble it but has different cleavage angles and often fluoresces yellow.
Because barium feldspar is uncommon and visually subtle, confident identification usually needs a specific-gravity measurement or lab analysis (XRF/EDS for barium).
Where It Is Found
Celsian and hyalophane occur in manganese-rich metamorphic and hydrothermal deposits and in some contact-metamorphosed rocks. Classic localities include Jakobsberg and Långban in Sweden, Broken Hill in Australia, Wales (Benallt mine), and manganese deposits in Japan and the western United States. Prospect within or adjacent to manganese ore bodies and barium-bearing skarns.
Frequently asked questions
What is barium feldspar?
Barium feldspar is a feldspar in which barium replaces potassium, spanning the celsian–hyalophane series. It looks like ordinary feldspar but is notably denser because of its barium content.
How do you tell barium feldspar from regular feldspar?
They look almost identical, so density is the key clue: barium-rich celsian has a specific gravity around 3.1–3.4 versus about 2.56 for K-feldspar. Reliable confirmation usually needs a specific-gravity measurement or chemical analysis for barium.
Is barium feldspar rare?
Yes. True barium feldspars like celsian are uncommon and mostly confined to manganese-rich metamorphic and hydrothermal deposits such as Långban in Sweden and Broken Hill in Australia.
What is the hardness of barium feldspar?
About 6 to 6.5 on the Mohs scale, the same as other feldspars. It scratches glass and shows two cleavage directions meeting near 90 degrees.