Lognormal distribution mean and standard deviation

I am performing a Monte-Carlo simulation and have an input parameter that follows a Log-normal distribution. Accompanying this parameter is a "Best Estimate" of the parameter value and "Distribution for a 90% likelihood range". The best estimate and likelihood range are given as negative values. I now need to use this data to establish the parameter mean and standard deviation (SD). I am taking the "best estimate" as the mean.

(a) How shall I interpret the negative values given that the accompanying distribution is Lognormal?
(b) How does once calculate the SD given the supplied information (likelihood range).