andesite
Enable an agent to recognise andesite, assess the condition and evidential basis of its identification, and determine suitable investigation or material use.
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 recognise andesite, assess the condition and evidential basis of its identification, and determine suitable investigation or material use.
Andesite is an intermediate volcanic igneous rock, typically fine-grained or porphyritic, composed chiefly of plagioclase feldspar with pyroxene, amphibole and sometimes biotite in a fine-grained or partly glassy groundmass.
It can be Record a provisional andesite identification with its supporting observations and unresolved alternatives.; Select petrographic or chemical investigation appropriate to the groundmass and alteration state.; Compare specimens while preserving differences between phenocrysts, groundmass, veins and weathered surfaces.; Choose samples that represent distinct textures and condition domains within an exposure or material lot.; Assess whether available test results support a proposed material use or require further testing..
Distinguishing features
Establish volcanic rock texture and origin; a broadly similar mineral composition alone does not distinguish andesite from a coarse-grained intrusive rock such as diorite.
Use an explicitly named petrographic or chemical classification scheme to distinguish andesite from basaltic andesite and dacite; colour alone is insufficient.
Check whether mineral proportions can actually be determined in the fine-grained groundmass before accepting a mineral-based classification.
Distinguish coherent andesite from fragmental deposits containing andesite clasts; clast identity does not automatically classify the whole deposit.
Check alteration before treating present mineralogy or whole-rock chemistry as evidence of the original rock composition.
Scope
+ Petrographic and chemical evidence supporting an andesite identification
+ Mineral assemblage, groundmass, crystal populations and volcanic textures
+ Alteration, weathering, vesicles, fractures and their effects on condition
+ Specimen, outcrop and material-lot provenance and representativeness
+ Evidence needed to assess andesite for geological interpretation or proposed material use
- Complete models of neighbouring rock kinds such as basalt, dacite and diorite
- Individual mineral species as independently registered things
- Whole volcanoes, magma systems and tectonic settings
- Eruptions and volcanic hazard management
- Quarry operations, manufactured aggregates and construction products
Characteristics
- Identification status
- field identification | laboratory-supported identification | disputed | unresolved Separates a provisional rock name from an identification supported by suitable observations.
- Classification basis
- Named scheme and version; petrographic, chemical or provisional field basis Makes the boundary with adjacent rock kinds explicit and reproducible.
- Whole-rock major-element composition
- Oxide mass percentages, analytical uncertainty, loss on ignition and normalization basis Supports chemical classification where texture limits mineral counting, subject to alteration and analytical quality.
- Mineral assemblage and proportions
- Identified phases and volume percentages where measurable; distinguish phenocrysts from groundmass Supports identification and prevents conspicuous crystals from being mistaken for the composition of the whole rock.
- Texture
- Groundmass grain size, crystallinity, phenocryst distribution, flow fabric and coherent or fragmental character Records volcanic fabric and determines which classification methods are feasible.
- Vesicle and fracture characteristics
- Vesicle volume percentage and size in mm; fracture spacing in mm or m, with orientation and connectivity Helps assess heterogeneity, fluid access and the relevance of intact-specimen measurements.
- Alteration and weathering
- Observed replacement minerals, oxidation, rind development and disaggregation; named grading method if used Affects classification reliability, preservation and material performance.
- Sampling context
- Links to collection location, geological unit, sampled domain, specimen and parent material lot Limits how far observations from one sample can be generalized.
- Measured material performance
- Density in kg/m³, water absorption in %, strength in MPa and use-specific durability results, each with method and specimen condition Supports decisions about a particular material rather than assuming performance from the andesite name.
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: 5 bundles · 9 layers · 15 findings · 23 questions.
Andesite identification Evidence and decision boundaries for applying the andesite name.
Andesite can be confused with neighbouring volcanic rocks or classified too confidently from appearance.
Classification evidence
The method, measurements and uncertainty behind the rock name.
Basis for the identification
Record how an andesite assignment was reached and whether the available evidence supports that method.
- Which classification scheme and observations support calling this material andesite? definition
- Can mineral proportions be measured reliably, or is whole-rock chemical analysis needed because of the fine groundmass? measurement
Neighbouring rock boundaries
Checks against adjacent compositions and similar-looking materials.
Alternative identifications
Preserve competing names until the observations discriminate between them.
- What evidence separates this material from basaltic andesite or dacite under the chosen scheme? boundary
- Does the texture support a volcanic rock identification, and is the named material a coherent rock or only a clast within a fragmental deposit? boundary
Mineral and textural fabric The mineral populations and groundmass that make up the observed andesite.
Visible crystals may represent only part of the rock, while groundmass and fabric control interpretation and sampling.
Crystals and groundmass
Separate observations of larger crystals from the finer material around them.
Phase populations
Record identified minerals, their proportions and where they occur without imposing a universal assemblage.
- Which minerals are identified in the phenocrysts and which in the groundmass, and by what method? measurement
- What proportions and grain-size distributions were measured, and which phases remain unresolved? measurement
Volcanic fabric
Crystallinity, flow structures, vesicles and inclusions within the rock.
Fabric and heterogeneity
Describe textural domains that may require separate observations or samples.
- How do crystallinity, vesicle abundance and flow fabric vary across the specimen or exposure? measurement
- Which inclusions, veins or contrasting bands should be recorded separately to avoid misrepresenting the host andesite? boundary
Geological and sample context Where the material came from and what portion of a geological occurrence it represents.
A loose specimen or selected hand sample cannot establish the identity or variability of an entire rock body.
Occurrence provenance
Traceable collection and occurrence information.
Source occurrence
Connect the identification to its actual collection context and distinguish observations from inherited labels.
- Was the material collected in place, as a loose fragment or from a supplied material lot, and where is that provenance recorded? provenance
- Which geological-unit and age assignments are supported by records, and which are merely inferred from location or appearance? provenance
Sampling representativeness
The extent to which a sample captures variation in its parent material.
Sample-to-body link
Define the physical domain to which each observation or analysis applies.
- Which fresh, weathered, vesicular or fractured domains does the sample represent, and which were excluded? boundary
- Where should additional samples be taken before extending this identification or performance result to the exposure or lot? action
Condition and material decisions How alteration and physical condition constrain interpretation and proposed use.
The andesite name alone does not establish preserved primary composition, strength or durability.
Alteration and weathering
Changes to minerals, chemistry and fabric after rock formation.
Preservation of primary evidence
Assess whether altered material still supports the proposed classification and measurements.
- Which minerals and textures show replacement, oxidation or weathering, and how extensive are those changes? measurement
- Does alteration make the current chemical classification uncertain enough to require a fresher sample or another identification method? action
Fitness for proposed use
Evidence required to decide whether a particular andesite material is suitable for an intended application.
Use-specific performance
Tie material decisions to measured performance, sample condition and the intended exposure.
- Which strength, absorption, abrasion or durability measurements are needed for the proposed use, and what methods and acceptance criteria apply? action
- Were the tested specimens representative of the supplied material's vesicles, fractures and alteration, under relevant moisture and exposure conditions? 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 describes the rock type, not a particular outcrop, commercial stone or volcanic deposit.
- The listed varieties overlap: mineral-based names and porphyritic texture describe different attributes.
- Silica content alone does not establish the rock name; classification, engineering suitability and hazards require sample-specific evidence.
- Which of these check these first hold for the sense of andesite this model covers, and on what evidence? provenance
Kinds and varieties
Recalled without web access and unsourced; every item is a lead to verify.
- Pyroxene andesite
- Hornblende andesite
- Biotite andesite
- Porphyritic andesite
- Which of these kinds and varieties hold for the sense of andesite this model covers, and on what evidence? provenance
Real-world use
Recalled without web access and unsourced; every item is a lead to verify.
- Crushed aggregate for roads and concrete where material quality meets project requirements
- Building stone, paving and masonry
- Investigation of volcanic processes and crustal evolution
- Which of these real-world use hold for the sense of andesite this model covers, and on what evidence? provenance
Typical measurements
Recalled without web access and unsourced; every item is a lead to verify.
- Silica content used in total alkali-silica classification - Approximately 57-63, subject to the total-alkali boundary of the andesite field - mass % SiO2 on an anhydrous basis
- Which of these typical measurements hold for the sense of andesite 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.
- Weathering and hydrothermal alteration can weaken the rock and reduce its suitability as aggregate or building stone.
- Joints, fractures and vesicles can reduce strength and promote water ingress or frost damage.
- Cutting or crushing material containing crystalline silica can generate hazardous respirable dust.
- Some volcanic glass or silica phases can contribute to alkali-silica reaction when the rock is used as concrete aggregate; testing is needed.
- Which of these failure modes and hazards hold for the sense of andesite this model covers, and on what evidence? provenance
Regional variation
Recalled without web access and unsourced; every item is a lead to verify.
- Common in subduction-related volcanic arcs, including the Andes and many Pacific island arcs, but not restricted to those settings.
- Mineral proportions, phenocryst abundance, vesicularity and alteration vary substantially among volcanic centres and individual flows.
- Which of these regional variation hold for the sense of andesite 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.
- Basaltic andesite - A neighbouring volcanic-rock class with lower silica content, conventionally about 52-57 mass % SiO2 in the relevant total alkali-silica field.
- Dacite - A more silica-rich neighbouring volcanic-rock class, distinguished using mineralogical or chemical classification.
- Diorite - The broadly corresponding coarse-grained plutonic rock; its texture records slower cooling beneath the surface.
- Trachyandesite - Distinguished chemically by higher total alkali content at comparable silica content.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of andesite this model covers, and on what evidence? provenance
What the second pass must settle
- Which authoritative classification scheme and exact compositional boundaries should govern this registry entry, including its treatment of basaltic andesite?
- Does an existing Vercy world model already own andesite or a rock classification model to which this entry should link?
- Which mineral assemblages and textures should researched guidance identify as common, optional or insufficient for diagnosing andesite?
- What evidence is sufficient to retain an andesite identification when alteration has obscured the original mineralogy or chemistry?
- Which intended material uses warrant dedicated assessment guidance, and which applicable test standards should that guidance reference?