obsidian
Enable an agent to identify obsidian as a natural volcanic glass, assess its condition and provenance, and judge its suitability for handling, analysis, working or conservation.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
recalled by Codex without web access - no source was read
Researched by: Codex
Purpose and description
Enable an agent to identify obsidian as a natural volcanic glass, assess its condition and provenance, and judge its suitability for handling, analysis, working or conservation.
Obsidian is a naturally occurring volcanic glass formed when lava, usually rich in silica, solidifies with little crystallization.
It can be Assess an obsidian identification using contextual, optical and analytical evidence.; Compare a specimen with geological reference materials and report source-attribution confidence.; Identify exposed sharp edges and choose protective handling and storage arrangements.; Evaluate whether cracks, inclusions and banding permit a proposed knapping or polishing operation.; Select an authorised sampling location that addresses the research question while limiting material loss.; Document alteration and determine whether cleaning, conservation or further examination is appropriate..
Distinguishing features
Require evidence of natural volcanic origin alongside glass identification; colour and lustre alone cannot separate obsidian from manufactured glass or slag.
Examine the matrix for predominantly glassy texture rather than the interlocking crystalline texture characteristic of many other igneous rocks.
Record conchoidal fracture and potentially very sharp edges as supporting evidence, while recognising that these features also occur in other glasses and chert.
Inspect vesicle abundance and distribution when distinguishing compact obsidian from highly vesicular volcanic glass such as pumice.
Use composition, hydration features and petrographic evidence when distinctions from pitchstone, perlite or other volcanic glasses remain uncertain.
Scope
+ Identification of natural volcanic glass and differentiation from visually similar materials
+ Composition, glass texture, inclusions and visible varieties
+ Geological origin, collection context and evidence for source attribution
+ Fracture behaviour, hydration, weathering and specimen condition
+ Material suitability for sampling, knapping, polishing, display and conservation
- Volcanoes, eruptions and lava flows as complete geological systems
- Manufactured glass, industrial slag and impact glass as separate material kinds
- Complete archaeological artefact typologies, cultural interpretation and ownership histories
- Finished jewellery designs and commercial product specifications
- Clinical performance or approval of instruments incorporating obsidian
- The Obsidian software application and its information-management functions
Characteristics
- Identification confidence
- unassessed | provisional | supported | disputed; supporting observations and methods Prevents a visual resemblance or seller label from becoming an unsupported material identification.
- Major-element composition
- oxide mass percentages; analytical method, uncertainty and normalisation basis Supports compositional classification and comparison without treating obsidian as a substance with one fixed chemical formula.
- Glass and crystalline constituents
- estimated glass and crystal fractions in volume percent, with method and uncertainty Helps distinguish a glass-dominated material from a crystalline rock and document partial crystallisation.
- Vesicle abundance
- volume percent where measured; otherwise a stated qualitative scale Informs identification, local weakness and comparison with other vesicular volcanic materials.
- Optical appearance
- observed colour, translucency, banding and sheen under specified lighting and specimen thickness Makes appearance reproducible and separates observations from variety names.
- Inclusion and banding texture
- observed crystals, spherulites, bubbles and flow bands; identification confidence Records internal features that can affect appearance, fracture and interpretation.
- Geological source attribution
- candidate outcrop or source population linked to comparison data, method and confidence Separates a tested source match from a collection locality or unverified provenance claim.
- Fracture and edge condition
- intact | chipped | fractured | edge-damaged; mapped cracks and exposed sharp edges Guides handling and determines whether working or sampling may propagate existing damage.
- Hydration-rind thickness
- micrometres; sampled surface, method, uncertainty and preparation history Records a surface alteration measurement without automatically converting it into an age.
- Alteration condition
- documented hydration, weathering, devitrification and surface deposits, with extent and evidence Distinguishes original material features from subsequent changes relevant to analysis and conservation.
Also called
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 17 findings · 27 questions.
Material identity Establish whether the material is obsidian and resolve its boundaries with similar glasses and rocks.
Obsidian can resemble manufactured glass and other natural materials, so recognition requires more than a dark glossy surface.
Volcanic glass identification
Connect observable glass texture with evidence of geological formation.
Evidence for obsidian identity
Record the observations and contextual evidence supporting a natural volcanic glass identification.
- What observations establish a glass-dominated matrix, and which require microscopy or other analysis? definition
- What evidence supports volcanic origin rather than manufacture, industrial processing or impact formation? provenance
Neighbouring material boundaries
Resolve ambiguous classifications involving other volcanic glasses and superficially similar rocks.
Differential identification
Record competing identifications and the evidence that could distinguish them.
- Which observations distinguish this specimen from chert, slag or manufactured glass when fracture and lustre overlap? boundary
- Which classification authority and specimen evidence resolve a possible boundary with pumice, perlite or pitchstone? boundary
Composition and texture Describe the glass matrix and internal features responsible for material variation.
Obsidian is compositionally and texturally variable; a single colour label cannot establish its properties or source.
Glass composition
Capture measured chemistry and the limits of the sampled material.
Analytical composition
Record composition with sufficient method information to support valid comparisons.
- What major-element composition was measured, in which units and using which analytical method? measurement
- Does the measurement represent fresh glass, an altered surface or a mixture containing inclusions? boundary
Internal and optical features
Describe crystals, bubbles, bands and optical effects without relying on trade terminology.
Texture and variety evidence
Separate observable features from proposed explanations and variety labels.
- What crystals, spherulites, vesicles or flow bands are present, and how are their abundance and distribution established? measurement
- What observed feature supports a label such as snowflake, rainbow or sheen obsidian, and is its physical cause verified? definition
Geological origin and source Connect the material to formation context, collection location and tested source attribution.
A specimen's collection site, geological origin and inferred archaeological source are distinct claims.
Formation and occurrence
Locate obsidian within its geological setting and distinguish primary from transported occurrences.
Occurrence context
Record the geological relationship of the sampled material to an outcrop, deposit or loose find.
- Was the specimen collected from an in-place volcanic unit, a secondary deposit or an undocumented location? provenance
- What mapped unit or formation evidence supports its origin, and how securely is that evidence linked to this specimen? provenance
Geochemical source attribution
Assess source comparisons using suitable reference coverage and comparable measurements.
Source match confidence
Represent source assignments as evidence-based comparisons with explicit alternatives and limits.
- Which reference source populations and measured elements were used to attribute this obsidian? provenance
- Do measurement uncertainty, within-source variation or missing candidate sources prevent a unique attribution? boundary
Fracture and alteration Record mechanical discontinuities and changes to the glass and its surfaces.
Sharp fracture edges, hydration and crystallisation affect handling, analytical interpretation and preservation.
Fracture condition
Assess cracks, flakes and edge damage at the scale relevant to the next action.
Cracks and sharp edges
Locate existing discontinuities and exposed edges that constrain handling or working.
- Where are open cracks, incipient flakes and sharp edges, and what observations establish their extent? measurement
- How should the specimen be supported and contained to avoid edge contact or propagation of existing fractures? action
Glass and surface alteration
Distinguish hydration, weathering and devitrification from original textures and later deposits.
Alteration evidence
Record observed alteration and constrain interpretations that depend on surface history.
- What measurements or observations distinguish hydration, devitrification, weathering and removable surface deposits? measurement
- If hydration is used to estimate age, what surface history, environmental assumptions and source-specific calibration support that estimate? provenance
Working, analysis and preservation Translate obsidian-specific observations into justified working, sampling and conservation decisions.
Knapping, polishing and sampling can change fracture surfaces or remove evidence needed for later interpretation.
Working suitability
Assess whether the material can support a proposed cutting, knapping or polishing operation.
Fit between operation and material
Connect the desired result to internal flaws, texture and the consequences of material removal.
- How do specimen dimensions, cracks, inclusions and banding constrain the proposed knapping or polishing operation? action
- What controls are needed for sharp fragments and generated dust during the specific operation? action
Evidence-preserving intervention
Choose analytical and conservation actions with awareness of diagnostic surfaces and irreversible changes.
Sampling and treatment choice
Record the purpose, authorisation and evidential consequences of sampling or treatment.
- Can the analytical question be answered without removing material, and if not, which authorised sample location preserves the most diagnostic evidence? action
- Would cleaning, coating or polishing modify a hydration surface, residue or fracture feature needed for future study? boundary
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Check these first
Recalled without web access and unsourced; every item is a lead to verify.
- This entry covers the geological material, not software or other products named Obsidian.
- Listed varieties are informal appearance or form categories, not separate mineral species; Apache tears are rounded obsidian nodules.
- Physical properties vary with composition and inclusions; hydration dating requires source-specific and environmental calibration.
- Which of these check these first hold for the sense of obsidian this model covers, and on what evidence? provenance
Kinds and varieties
Recalled without web access and unsourced; every item is a lead to verify.
- Black obsidian
- Mahogany obsidian
- Snowflake obsidian
- Rainbow obsidian
- Sheen obsidian
- Apache tears
- Which of these kinds and varieties hold for the sense of obsidian this model covers, and on what evidence? provenance
Real-world use
Recalled without web access and unsourced; every item is a lead to verify.
- Knapped cutting tools, projectile points and scrapers.
- Jewellery, beads, carvings and ornamental objects.
- Specialized blades for research and some surgical applications.
- Archaeological sourcing through comparison of elemental composition with known geological deposits.
- Obsidian hydration dating under conditions that account for environmental and material differences.
- Which of these real-world use hold for the sense of obsidian this model covers, and on what evidence? provenance
Typical measurements
Recalled without web access and unsourced; every item is a lead to verify.
- Mohs hardness - 5-5.5 - Mohs scale
- Density - 2.3-2.6 - g/cm³
- Which of these typical measurements hold for the sense of obsidian this model covers, and on what evidence? provenance
Failure modes and hazards
Recalled without web access and unsourced; every item is a lead to verify.
- Brittle conchoidal fracture produces extremely sharp edges and fragments that can cause cuts.
- Impact or bending can chip or break tools and decorative objects.
- Knapping, cutting and grinding can eject fragments that injure eyes.
- Cutting and grinding generate dust requiring exposure control; its composition depends on the specimen.
- Hydration, weathering and devitrification can alter the glass over geological time.
- Which of these failure modes and hazards hold for the sense of obsidian this model covers, and on what evidence? provenance
Regional variation
Recalled without web access and unsourced; every item is a lead to verify.
- Deposits occur in volcanic regions including Iceland, the Mediterranean, East Africa, Japan and the Americas.
- Elemental composition varies among volcanic sources, enabling archaeological provenance studies where suitable reference data exist.
- Colour, inclusions and optical effects vary among deposits; many variety names are informal trade terms.
- Which of these regional variation hold for the sense of obsidian this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Recalled without web access and unsourced; every item is a lead to verify.
- Rhyolite - Rhyolite denotes a silica-rich volcanic rock composition; obsidian denotes a predominantly glassy material, often of rhyolitic composition.
- Pumice - Pumice is strongly vesicular volcanic material, whereas typical obsidian is compact and has relatively few bubbles.
- Pitchstone - Pitchstone is volcanic glass generally distinguished by greater water content and a resinous rather than strongly glassy lustre.
- Tektite - Tektites are natural glasses formed from terrestrial material during meteorite impacts; obsidian forms through volcanic processes.
- Manufactured glass - Manufactured glass is produced by human processing; obsidian is naturally formed volcanic glass.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of obsidian this model covers, and on what evidence? provenance
What the second pass must settle
- Which geological classification authority should govern ambiguous boundaries between obsidian, pitchstone, perlite and partly crystallised volcanic glass?
- Which named obsidian varieties have well-supported diagnostic criteria, and which should remain unverified trade labels?
- Which source-reference datasets provide adequate geographical coverage and comparable analytical methods for the intended catalogue?
- Under what documented conditions can hydration measurements support age estimates, and how should their uncertainty be represented?
- Which conservation guidance and working procedures should govern obsidian specimens with fragile edges, altered surfaces or archaeological evidence?