The 200kg of concentrate was produced after production from a pilot plant was reprocessed through a polishing circuit, with samples now being sent to potential customers for assessment.
Black Rock said the "value proposition" for high-grade concentrate had recently been made by Syrah Resources, which is reportedly now targeting grades of 97-98%.
"Being able to generate ultra-high grade product using flotation is of significant value to downstream processors who are increasingly finding environmental constraints impacting their business," Black Rock said.
The junior is aiming to complete a definitive feasibility study later this year and be commissioning a graphite operation by late next year.
A prefeasibility study outlined a long-life project with initial capex of US$90 million and above-the-line earnings in the first full year of production of $220 million.
Black Rock started the current quarter with A$3.2 million cash.
Shares in Black Rock closed Monday at 4.6c, capitalising the company at $20.4 million.
The stock has traded in a range of about 5-7c for much of the past year.