amorphous Mineraloids

Moldavite (Natural Tektite)

Formula SiO2-rich glass (>70 wt% SiO2) + Al2O3, MgO, FeO, CaO, K2O, Na2O (natural impact glass; composition variable)

Crystal Structure

CDL Notation

 #! Species: Moldavite (tektite glass; non-IMA)
#! System: Amorphous (impactite glass)
#! Habit: Irregular sculptured masses from aerodynamic ablation
amorphous[glassy]:{massive}

Crystal System amorphous

Point Group none

Crystal Forms (1)

{massive}

Quick Facts

Hardness

5.0

Specific Gravity

2.32

Refractive Index

1.48

Optical Character

Isotropic

Physical Properties

Crystal System: amorphous
Hardness (Mohs): 5.0
Specific Gravity: 2.32
Cleavage: None
Fracture: Conchoidal
Lustre: Vitreous to greasy

Optical Properties

Refractive Index: 1.48
Optical Character: Isotropic
Pleochroism: None

Characteristics

Colours

Bottle green to olive green (Fe2+ in glass)Brownish-greenRarely pale green

Localities

Czech Republic (south and west Bohemia, southern Moravia; primary strewn field)Germany (Ries crater area, Bavaria; Nördlingen Ries bolide impact ~14.7 Ma)Poland (rare re-deposited specimens)

Common Inclusions

Lechatelierite (pure silica glass schlieren and tubes; diagnostic of high-temperature fusion)Gas bubbles (round to elongated)Occasional relict mineral grains (zircon, chromite) from target rocks

Known Treatments

Minimal (cleaning and polishing)[object Object]

Crystal Forms

massiveirregular

Diagnostic Features

Characteristic wrinkled/pitted/sculptured surface (aerodynamic ablation during atmospheric flight after Ries impact); schlieren (flow banding) under magnification; elongated gas bubbles; SG 2.32-2.38 (lower than obsidian 2.40-2.55); RI 1.480-1.510; bottle-green colour from Fe2+

Notes

Natural tektite (impactite glass); NOT an IMA mineral species (tektites are not crystalline minerals per IMA definition). Formed by Nördlingen Ries bolide impact, southeastern Germany, ~14.7 Ma; strewn field in Bohemia and Moravia, Czech Republic. Included in mineral-DB as gem material per FGA Foundation/Diploma curriculum coverage. Per VERIFIED.md decision: ship as amorphous entry with clear notes that it is a non-IMA species (same convention as opal which is also amorphous). IMA-approved: No. Tektite strewn-field research: (DOI 10.3190/jgeosci.214) [PARTIALLY_SUPPORTED]. Gem localities context: Shigley et al. 2000 (DOI 10.5741/gems.36.4.292) [VERIFIED]. SG 2.32-2.38 lower than obsidian (2.40-2.55); RI 1.480-1.510 from Read 7th ed. (DOI 10.4324/9780080507224) [PARTIALLY_SUPPORTED].