Xonotlite is a hydrous calcium silicate typically found as dense, fibrous masses or radiating needle-like clusters. It is highly valued by collectors for its fine, silky texture and often forms in high-temperature contact metamorphic environments.
Is this xonotlite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch xonotlite with a known reference. Xonotlite sits at Mohs 6-6.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly, greasy.
- 4Match the color rangeCompare against the expected color range: colorless, gray, lemon white, light gray, pink.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular, massive.
Often confused with
Xonotlite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Xonotlite is noticeably harder (Mohs 6-6.5 vs. 4.5-5); luster reads pearly, greasy on Xonotlite and vitreous, pearly on cleavage on Wollastonite.
How to tell apart: Xonotlite is noticeably harder (Mohs 6-6.5 vs. 4.5-5); luster reads pearly, greasy on Xonotlite and silky, subvitreous on Pectolite.
How to tell apart: Luster reads pearly, greasy on Xonotlite and vitreous on Tremolite.
Often found alongside xonotlite
Minerals reported to co-occur with xonotlite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₆Si₆O₁₇(OH)₂
- Mohs hardness
- 6-6.5
- Density
- 2.71-2.72 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly, greasy
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular, massive
- Cleavage
- Perfect in one fh0lg direction
- Fluorescence
- Weak gray-white under SW UV; weak white under LW UV
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- In contact metamorphic deposits within limestones, serpentinites, and metavolcanic rocks
Where rockhounds find xonotlite
Classic worldwide localities
- Leesburg, Loudoun Co., Virginia, USA
- Franklin, Sussex Co., New Jersey, USA
- Hunting Hill quarry, Rockland, Montgomery Co., Maryland, USA
- Isle Royale, Lake Superior, Michigan, USA
- Tetela de Xonotla, Puebla, Mexico
- Point Shivery, Bay of Islands, Newfoundland, Canada
Field-hunting tip
Where it forms: In contact metamorphic deposits within limestones, serpentinites, and metavolcanic rocks. If you start seeing tobermorite, clinohedrite, wollastonite in float, you are in the right ground. Typical habit: acicular, massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify xonotlite?+
Where is xonotlite found?+
What rocks look like xonotlite?+
What minerals are found with xonotlite?+
What kind of rock does xonotlite form in?+
What is xonotlite used for?+
Find xonotlite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
