Class <<DataType>> ConstituentPart

<xs:element xmlns:xs="http://www.w3.org/2001/XMLSchema" name="ConstituentPart" type="gsml:ConstituentPartType">
    <xs:annotation>
        <xs:documentation>The Constituent Part class describes how Earth Materials may be made up of other Earth Materials, including the proportion of the constituent part in the whole (eg: 20%, minor, dominant); the role that the constituent plays in the whole (eg: matrix, groundmass, framework, phenocryst, xenolith, vein). The particleType property that specifies type of particle (eg: grain, clast, crystal, fossil, oolite) has been moved to the ParticleGeometryDescription data type, associated with both ConstituentPart and CompoundMaterial (GeoSciMLv2, RC3, Uppsala, Sweden).

The distinction between "role" and "particleType" is subtle.  An operational test is that constituentType may be determined independent of relationship between particles in the aggregation, whereas role requires consideration of the relationship to other particles. A particle may be identified as clast, independent of its material composition, and independent of its relationship to other grains in a rock. The term 'floating clast' is a role, because it is dependent on the relationship 'not in contact with other clasts'. Consider Dunham's textural classification of carbonate rocks (wackestone, packstone, grainstone...) in the description of carbonate rocks. The description is predicated on identification of two kinds of intraclasts (grains) and matrix (carbonate mud), and then uses this distinction to establish relationships--mud supported vs. grain supported -- that define roles for the two types of constituents (framework, matrix...).

examples of type vs. role:
Particle type: clast. Role: framework, floating particle

particle type: crystal. Role: matrix, pseudomatrix (in case that matrix is interpreted as recrystallized material)

particle type: clast. Role: matrix (in case that matrix is interpreted as very-fine grained detrital fraction)

particle type: crystal. Role: cement (in case that material insterstitial to particles is crystalline material introduced during diagenesis)

particle type: crystal. Role: phenocryst (in igneous rock)

particle type: microlite Role: groundmass (in porphyrytic igneous rock)

particle type: crystal. Role: framework (in igneous rock)

particle type: pyroclast. role: framework (in tuff)

particle type: crystal Role: oikocryst

particle type: crystal Role: overgrowth

particle type: biogenic particle Role: floating particle

particle type: ooid Role: framework</xs:documentation>
    </xs:annotation>
</xs:element>

<xs:complexType xmlns:xs="http://www.w3.org/2001/XMLSchema" name="ConstituentPartType">
    <xs:sequence>
        <xs:element name="proportion" type="gsml:CGI_ValuePropertyType">
            <xs:annotation>
                <xs:documentation>The fraction of the whole that is formed by a ConstituentPart in a part/whole relationship.  Used for the ConstituentPart portion in a CompoundMaterial. 

Quantity that specifies the fraction of the Earth Material formed by the part (eg: 20%, minor, dominant)</xs:documentation>
            </xs:annotation>
        </xs:element>
        <xs:element name="role" type="cgu:CodeWithAuthorityType">
            <xs:annotation>
                <xs:documentation>The role a ConstituentPart plays in a CompoundMaterial aggregation.   The same EarthMaterial may occur as different ConstituentParts playing different roles within the same CompoundMaterial.  For example, feldspar may be present as groundmass (a ConstituentPart::role) and as phenocrysts (an ConstituentPart::role) within a single igneous rock.</xs:documentation>
            </xs:annotation>
        </xs:element>
        <xs:element maxOccurs="1" minOccurs="0" name="material" type="gsml:EarthMaterialPropertyType"/>
    </xs:sequence>
</xs:complexType>

<xs:complexType xmlns:xs="http://www.w3.org/2001/XMLSchema" name="ConstituentPartPropertyType">
    <xs:sequence>
        <xs:element ref="gsml:ConstituentPart"/>
    </xs:sequence>
</xs:complexType>