ZTR Index
Definition
Zircon-Tourmaline-Rutile index: [(zircon + tourmaline + rutile)/total transparent non-opaques] x 100. High values mark texturally and chemically mature sediments that have lost less stable minerals through weathering and reworking.
- Full name
- Zircon-Tourmaline-Rutile index
- Formula
- (zircon+tourmaline+rutile)/total transparent non-opaques x 100
- Measures
- Sediment maturity
- High value means
- Loss of less-stable minerals via weathering/reworking
Common questions
Why is ZTR index useful in trace evidence comparison?+
Soil or dust samples with similar ZTR values point to source sediments of comparable maturity and weathering history, helping an examiner support or exclude a proposed link between a questioned soil sample and a scene location.
What minerals count toward the total but not the ZTR numerator?+
Less stable transparent heavy minerals such as amphiboles, pyroxenes and epidote are included in the total non-opaque count used as the denominator but are excluded from the numerator, since their presence lowers the index.
Related terms
- ATi Index
- Apatite to Tourmaline index: [apatite/(apatite + tourmaline)] x 100. Low values indicate advanced weathering or sediment recycling because apatite is dissolved by...
- Bromoform (CHBr3)
- Tribromomethane, density 2.89 g/cm3, historically the standard heavy-separation liquid. Now largely displaced by sodium polytungstate because of its toxicity and regulatory requirements,...
- Heavy Minerals
- Minerals with density greater than 2.85 g/cm3, separated from a soil or sediment by a heavy liquid. They typically form 0.1-5% of...
- Provenance
- The documented origin of a media file: the device that captured it, the time and location of capture, the chain of custody...
- Sodium Polytungstate (SPT)
- An aqueous inorganic salt solution used as a non-toxic alternative to bromoform for density separation. Density is tunable by concentration; the 2.85-2.90...