Tanganyika Trading was founded by Hilmar Bosch in 1961, originally operating out of Zimbabwe, Africa. From the very beginning, Hilmar worked closely with elite cutting houses in Idar-Oberstein, Germany, supplying high-quality gemstone rough from Mozambique, Zambia, and Zimbabwe.

In 1982, Hilmar and his family emigrated to South Africa, where he expanded his gemstone rough business and pioneered international mail-order trading of facet-grade rough. An early adopter of digital technology, Hilmar launched one of Africa’s first gemstone websites in the early 1990s—long before most in the industry had left behind paper price lists and catalogues.

Today, Tanganyika Trading supplies premium facet-grade rough to lapidaries, carvers, and jewellers across the globe. Our sourcing network has expanded far beyond the original three countries, and now includes Mozambique, Namibia, Malawi, Tanzania, Nigeria, Kenya, Zambia, Madagascar, Brazil, Bolivia, and Zimbabwe. We ship worldwide and are proud to serve a loyal customer base built on trust, transparency, and deep-rooted expertise.

We believe in supporting both master and independent lapidaries by offering carefully selected rough with high clarity and honest disclosure. Whenever possible, we share the full story of each stone—origin, treatments, colour, and clarity—so you can cut and create with confidence.

About Us

Hilmar Bosch – Founder

Of Dutch nationality, I was born in Nairobi, Kenya, and spent my early years travelling across Africa with my parents. After completing my education in Harare, Zimbabwe (then Rhodesia), I began studying geology at university but soon realised my true calling was gemstones. In 1963, I left to pursue gemmology full-time, earning my Fellowship Diploma from the Gemmological Association of Great Britain.

I went on to establish and teach the first Gemmology and Gemstone Cutting courses at Harare Polytechnic, while running our jewellery and gem-cutting factory. Over the decades, I built strong relationships with German cutting houses in Idar-Oberstein, who purchased our tourmaline, topaz, aquamarine, and garnet rough, while bulk materials like agate, carnelian, and fossilised wood found ready markets in the USA.

In 1982, following political unrest in Zimbabwe, I relocated to South Africa and launched African Gemstones, later founding Tanganyika Trading in 1994 to focus on our Tanzanian gemstone supply. Both businesses have since been consolidated under one banner — Tanganyika Trading, now found at: tanganyikatrading.com 

Michael Howard Lewis – Next Generation

Born and raised in Zimbabwe, Mike Lewis first dabbled in gemstones as a teenager, making all the usual beginner mistakes that ultimately sparked a deeper passion for the trade. He began his formal training with an introductory course through GEM-A before enrolling in the German Gemmological Association (DGemG) in Idar-Oberstein in 2015, earning the title F.G.G. (Fellow of the German Gemmological Association).

In 2024, Mike completed the Graduate Gemologist (G.G.) program through GIA, and also studied rough diamond evaluation at the Harry Oppenheimer Diamond Training School in South Africa. Based in London, UK, Mike has worked in both the retail and wholesale gem & jewellery industry, and now joins Tanganyika Trading under Hilmar’s mentorship to carry the legacy forward with integrity, enthusiasm, and fresh perspective.