Natural Science in Archaeology

2.3 Mineral Identifi cation Methods 21
type of fracture observed in glass and the mineral quartz. Some minerals exhibit
a fibrous or splintery fracture. A hackly fracture results in jagged and sharp edges.
Fractures producing rough and irregular surfaces are called irregular fractures. The
most common fracture for the production of lithics is the conchoidal fracture exhibited
by obsidian, chert, quartz, and quartzite.
The term luster refers to the appearance of a mineral surface in reflected light.
Metallic luster is that of a shiny metal. Minerals with a metallic luster are opaque.
Galena and pyrite are common minerals with a metallic luster. A metallic luster has also
been added artificially to give decorative effects to glazed ceramics. This technique was
created by Arab ceramists in the ninth century (Darque-Ceretti et al. 2005) and spread
over the Mediterranean basin especially to Spain and Italy. This technique is based on
firing of the glazed pottery in a reducing atmosphere in the presence of metallic salts.
This produced a metallic-appearing surface with a gold, brown, or red luster. The luster
was a result of metal particles of nanometer size dispersed in a glassy matrix.
Minerals with a nonmetallic luster are generally light-colored and transmit light, at
least through thin edges. The following are the important types of nonmetallic luster:
Vitreous: The luster of glass. Example: quartz.
Pearly: An iridescent pearl-like luster, usually observed on mineral surfaces
that are parallel to cleavage planes. Example: cleavage surface of talc.
Greasy: Appears as if covered with a thin layer of oil, resulting from light
scattered by a microscopically rough surface. Examples: some
specimens of sphalerite and massive quartz.
Silky: Silk-like, caused by the reflection of light from a fine fibrous
parallel aggregate. Examples: fibrous gypsum and serpentine.
Adamantine: A hard, brilliant luster like that of a diamond, due to the mineral’s
high index of refraction. Example: the transparent lead mineral
cerussite.
See Sect. 2.4 for further information about the causes of luster in minerals.
2.3 Mineral Identification Methods
2.3.1 Element Analyses
Modern instrumental techniques are all capable of multi-element analysis. These
techniques can be used to determine well over half of the elements in the Periodic
Table. They provide high precision and accuracy over a range of elemental concentrations.
However, each technique has one or more limitations, so one must evaluate
the relative merits of the competing systems. Most are destructive so not applicable
to museum specimens. Detailed explanations of these instruments and instrumental
techniques are readily available in all libraries (for example, see Ewing 1997).