142 SURFACE LUSTRE
Surface lustre
M
ost gems have a vitreous lustre – their surface reflects
light like glass. A few are metallic or adamantine (like a
diamond). More rarely, gems may glimmer like silk or look
matt, not shiny. Some feel greasy or waxy to the touch, while
organic gems may be resinous or pearly. Lustre is subjective –
judged by sight or touch rather than scientific criteria.Diamond
Polished stones have an
adamantine lustre, while rough
stones may exhibit a greasy lustre.Gold
Gold has a metallic lustre,
which is opaque and
reflective. It does not
tarnish or discolour.Tsavorite garnet
An extremely rare gem, tsavorite
has a vitreous lustre, bordering
on adamantine.Citrine
A form of crystalline quartz,
citrine displays a classic
vitreous lustre.Amethyst
In common with most
other silicates, amethyst
has a vitreous lustre.Howlite
Howlite has a subvitreous
lustre – not quite or only
partly vitreous.Jadeite
Jadeite has a greasy or oily
lustre, which can occur if a
mineral has a huge number
of microscopic inclusions.142-143_FEA_Lustre.indd 142 19/05/2016 14:47