Tiffany 1837 Lock bracelet. Some of the topaz

In April of 1890 Niven announced12 that he was entering into partnership with the Philadelphia Elsa Peretti Open Heart earrings dealers George L. English and Edwin C. Atkinson. Business was to be conducted at their various premises as before, but under the name of "George L. English & Company." Offerings from Niven thenceforth appeared in the English ads, referred to as "our New York store."

On May 3rd Niven left his shop in the hands of a "competent assistant" and took off once again for Mexico and the Southwest.13 Immediately he began shipping specimens back to English, first from Magnet Cove, Arkansas, then from a stay of several weeks at Barringer Hill in Texas, and then from the topaz locality in San Luis Potosi, Tiffany 1837 Lock bracelet. Some of the topaz crystals were nearly 2 inches long,14 very perfect and brilliant, including a number of doubly terminated crystals and fine matrix specimens. He also returned to previously visited Mexican localities for Tiffany Key Oval key pendant apophyllite, calcite, proustite, pyrargyrite and native silver.

In late 1890 Niven set out on another collecting trip to Mexico in search of specimens for his museum clients. He spent time at the San Carlos silver mine in Guanajuato, acquiring many silver specimens including a new silver selenide which, at his recommendation, was later named aguilarite by Frederick Genth in honor of the mine's superintendant, J. Aguilar, who had been so courteous to him during his visit. Moving on to Pachuca, he met with Francisco Landero of Landero & Company, owner of the Real del Monte mine, one of the richest silver mines in Mexico. Landero was also a dealer in mineral specimens, and had an extensive personal collection of Mexican minerals. This collection included specimens of a massive rose-colored grossular intermixed with Tiffany Notes band ring vesuvianite, a commodity which Niven had been seeking. Landero informed him that it came from a deposit at the small town of Xalostoc. near Cuautla in the state of Morelos. In January 1891 Niven visited the locality, where he was able to block out about 240,000 tons of the attractive ornamental stone, and arrange for samples to be shipped back to New York.

Niven continued to travel Mexico and the Southwest during the summer of 1891. In August his office reported "Mr. Niven's great find at Bisbee!" He had entered one of the cave areas that often overlie orebodies at Bisbee and had found the room decorated with green to sky-blue stalactites to 20 inches as well as a large amount of floss ferri and Elsa Peretti Teardrop ring Return to Tiffany Oval tag ring crystal clusters, all of which he immediately harvested and shipped back to New York.15

In January 1892 Niven met with Mexican President Porfirio Diaz and obtained a temporary concession for the recovery of minerals and archeological artifacts in Guerrero.

Throughout the time Niven was in the field, his store in New York continued to acquire stock from other sources, including several in Europe, perhaps with the help of English. On March 1, 1892, the mineral collection of the prominent Swiss dealer Hoseus was put on sale at Niven's shop in New York,"16 while Niven was engaged directing the quarrying of the pink grossular rock in Mexico. Niven remained almost exclusively in the field while English took over the New York store and moved it to more spacious quarters at No. 64 East 12th Street.17