African Natural Ruby (Mix)

Buying this parcel

Where it came from, what its weight band is for, and what to check before any money changes hands.

The deposit

African ruby now means Mozambique first. The Montepuez deposit in Cabo Delgado opened in 2009 and within a few years supplied more fine ruby by weight than any other source on earth, with Tanzania at Winza and Songea and the John Saul mine in Kenya making up most of the rest. Montepuez material is amphibole-hosted rather than marble-hosted, so it carries more iron than Burmese ruby. That damps the fluorescent glow but tends to come with better clarity and a more even colour distribution through the crystal, which in small stones matters more than glow does.

This parcel

One to four carats is the accent range, and it is bought for a different job than a single centre stone. These are the stones that become the side pair on a ring, the row in a bangle, or a set of nine in a Navratna mount where every stone has to sit at a similar tone. The buying problem in this band is never finding one good stone, it is finding six that match. Tell us the count and the tone you are matching to and we will select against that, because a parcel picked for an average will give you a spread rather than a set.

Treatment

Mozambique ruby is routinely heated at low temperature to clean up the blue patches that occur naturally in the rough, and that is disclosed, permanent and priced in across the trade. This parcel is not heated, which in a small-stone band is less common than it sounds, since heating is cheapest to justify on exactly this kind of material. The other treatment that circulates in African goods is glass filling in the lower grades. It is easy to spot in quantity because filled stones show flash effects along their fractures when rocked under a light.

The report

No report is held for this 1 to 4 cts ruby parcel yet, and we would rather say that than name a laboratory that has not seen it. We will submit whatever you select to IGI or IIGJ before purchase on request.

Before you pay

• Ask to see the parcel poured out rather than a selected handful, and pull stones at random from the middle of it.
• Check colour consistency by laying candidate stones on white paper side by side, not one at a time against your hand.
• Rock a few under a point light and look for the orange or blue flash that gives away a filled fracture.

Read next

Manikya, the ruby covers the material itself and what gets sold in its place. How to buy a coloured stone covers pricing, treatment and reports.

Written by Kamal Kishore Agarwal, founder and gemmologist, Gem-A qualified, buying in Johari Bazaar since 2008.